2lbs a week is excessive and unsustainable under most circumstances. More so while training hard.

I'm 5'10 (1.78m). I weigh about 82.5kg (182lbs) at present. I aim to reach 81kg (178.5lbs) in the next 6 weeks before my B event and 79.5kg (175lbs)within 12 weeks before my A event. That's an average of about 250g (8.8oz) a week. That's a modest weight loss and is definitely feasible, but not easy. I could of course aim to lose more, but based on experience this is a realistic and achievable target. If I do better, great.
Would I be faster at 75kg? Yes. But it's likely not currently feasible without misery and compromised training. Further reductions are an ongoing goal and 75kg is a potential goal for winter or next year. I have a race in 6 weeks and another in 10 weeks, that doesn't preclude long term planning.

You're probably a better runner by doing more volume, assuming you are also doing enough bike and swim volume. The OP stated that he is restricted to no more than 25 miles per week. Those are the constraints under which any advice you can give to him. You certainly can go sub 4 on 25 miles of run training, assuming you have swim and bike fitness, and are light.

Having said that, you are not maximizing your running potential based on your current fitness. Quite frankly, 178 is huge and a lot of weight to carry around in a marathon or ironman, particularly at 5'10. You are wasting your training. You should aim for max weight of 157.

You're joking. If you can't lose weight off ironman training 10 weeks out from the race, then you just don't want to maximize your potential based on your fitness level. The OP will only increase his chances of reaching his potential; not even close to sabotaging it.

What are your race times?

Relevance?.... or are you attempting to construct an appeal to authority?

No dude. You are flat out wrong. You want to lose .5 pounds per week, good. Any athlete should be okay with that.

You want to try to up it to lose 1.5 pounds per week? You are going to fuck your training, your mood, hormones, etc. don't be an idiot.

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New Training/Racing Log - http://www.earthdaykid.com/blog --- Old Training/Racing Log - http://colinlaughery.blogspot.com

Ok, I guess it's settled then! Thanks for enlightening me.

When you weigh 170-190 lbs, something is wrong with your diet and you are not reaching your potential based off your training. Losing 1.5 pounds per week at that weight is pretty easy and will not screw at all with your training, mood, or hormones; to the contrary you'll eat better, eat the the right foods, and eat only what you need, and as a result, start training better, with more energy, and more effectively.

Lance Armstrong: “I was a swimmer and I was always stuck with a swimmer’s body,” says Armstrong, who started his competitive life as a triathlete and retained a heavily muscled upper body. It was a build well suited to winning one-day races, but which proved a liability in multi-week tours studded with long climbing stages. When Armstrong returned to cycling after his bout with cancer, he was 20 pounds lighter and worlds faster on the climbs.
“Being lean is all about the three or four months before the Tour and—let’s be honest here—this is just about starvation,” he says. “For me to get down to 163 pounds and still be four percent [body fat]? I’ll tell you, in those months leading up to the Tour, you’re just hungry, man.”
https://www.outsideonline.com/...france-riders-really

Meb Keflezighi: Famed marathoner Meb Keflezighi has already gained more than 12 pounds in the 10 days since he ran the 2015 Boston Marathon.

During training leading up to a race, Keflezighi said he runs 100 to 130 miles per week. He eats only two meals a day, skips sugary desserts and drinks 32 ounces of water before dinner to fill his stomach.
Afterward, he eats three meals a day and can treat himself to things like omelettes with bell peppers and cheese, ice cream and strawberry cheesecake.

http://abcnews.go.com/Health/guess-weight-famous-boston-marathoner-gained-10-days/story?id=30707421

Chris Froome: In the years leading up to that remarkable performance, Froome had been carrying all kinds of extra weight — tipping the scales at up to 167 pounds. In a 2014 interview with Paul Kimmage for the Irish Independent, Froome said he had "always been aware of the weight issue" but took it for granted: "I don't think I necessarily thought that I could go much lower than [69 kilos/152 pounds] and apparently I have. I've gone a good three kilos lower [66 kilos/145 pounds] which is huge."

Michelle Cound, now Froome's wife, said in the same interview that he "starved himself" before his breakout performance:
MC: He starved himself before the Vuelta, and then he came back to South Africa and that's when we started dating. I've always had a bit of an interest in sports nutrition and my view was that he could still train on more protein and cutting back on the carbs at certain times. And also making sure he wasn't hungry, so having more meals, more often, things like that.
http://www.businessinsider.com/chris-froome-weight-loss-tour-de-france-2016-7

Nope, just trying to help: I'm simply saying that you are doing yourself a disservice based on the amount of training you do by racing at that weight (and I assume you want to do well by having A races and the amount that you train).

As I think would be clear from my previous posts, I'm aware that I'm heavier than is ideal and aim to drop some weight. I have already reduced my weight significantly but have a bit further to go. My point was not about ideal racing weight but about your suggested rate of loss which I consider excessive.
I don't intend to try and get as light as you propose but I do intend to lose another 5-7.5kg (11-16.5lbs). Why? Because that will put me at a perfectly healthy weight and I don't feel the need to go any further. Amongst other things, excessive weight loss is liable to interfere with my stunning good looks. The gaunt face look doesn't work on me.

I reserve the right to change my mind at some later date.

Yes, I want to do well. But that is defined more by continuously improving rather than winning races. Everything is relative.

so perhaps its more intelligible to do shorter distance races. then again you can look at how lars did a 9hr IM with 9 hours of training.... more intense work. not much easy pace stuff.

Swimming/cycling responds well to hard work/volume. Running fast requires talent. Talent is rare, hard work ethic is a lot more common.

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Next races on the schedule: none at the moment

Do you mean more intelligent to do short races? If so, the answer is no. Both are still feasible so you do whichever takes your fancy. You can be probably place better in a shorter race for less volume. but that doesn't matter if it's not the event you enjoy most.
Low volume/high intensity does seem to work well for some to achieve fast times but I suspect this is due to strong base fitness built up over years. I seriously doubt this can be sustained over a career or produced by a newcomer. For most of us, lower volume means we'll need to accept slower times. I can live with that. I still intend to improve year on year.