I just went back through our communications on this thread to make sure I had all the info fresh on my brain. I've dropped in some quotes just to make sure there are no typos hidden in here. You started with a "stack" of 691 and and a "reach" of 534 (165 crank) and the idea of... "I want to go lower in the future".
My response to that was...
For the 2019 Speedmax SLX.........That bike will be a size Large.....etc. etc..
Then you can back with more info - seat height of 705, and then we knew it had to be a size medium.
Something seemed off to me and I inquired and you responded
The numbers I walked out the door with are not the pad x/y numbers
Now, we're going forward with a formula based off your overall height and your saddle height. So, with a seat height of 705mm and an overall height of 1702mm (5'7") I'd predict your Pad Y at 596 and your Pad X at 463.
If that prediction is correct (more on that below) then you have two ways to go...
2019 Speedmax SLX size M with a short stem, the TSP to pull pads a bit more, the flat bar, and....wait for it....slammed, which is to say no spacers under the aerobars.
2019 Speedmax SLX size S with a short stem, flat bar, pads back just a bit from the middle and in the stock mount holes (so, no TSP), and 30mm of aerobar pedestal.
Let's stop right here for one second. I'm slightly nervous because of where we started. We started with "stack of 691 and reach of 534". The fit business has this bit of confusion over these terms Stack 'n Reach vs. Pad Y 'n Pad X. Two very different things: Stack/Reach being the measurement to the top of the frame's head tube (used by fitters to size a mortal bike), and Pad Y/Pad X being the measurement to the arm pads (used by fitters to prescribe a super bike). What happens on this thread, and elsewhere in life, is that folks come forward saying "stack and reach" but really mean Pad Y/Pad X. This is so common that I took your first post to mean Pad Y/X. If you're telling me - "ignore that set of 691/534 numbers. Let's go with your prescription off the overall height/seat height to prescribe Pad Y/Pad X" then great. I'm confident! For your height, the prescription of 596/463 falls into an orthodox position - meaning that's where the vast majority of folks your height with your seat height ride. Just like if we both go in to get a vasectomy together, the doc's not going to cut into your scrotum and my abdomen. Not unless I was deformed at birth and somehow my vas deference is up around my small intestine. If I'm pretty normal and you're pretty normal we're both gonna take on the responsibility of birth control with the same, simple incision in the same place. If you're pretty normal then your Pad Y is around 596 and your Pad X is 463. PS. I've had mine done, it was great, I should have had that done at age 13. I'll still go with you to the appointment if you want because I know all of humanities issues can be solved by lowering the Earth's population. But I digress.
Okay, back to it.....you're ready to buy and, assuming you're in the U.S., I think we're gonna see bikes available soon, so let's get down to the nitty gritty. If you buy a Medium you're in a pretty extreme corner of that bike: slammed, so you can not go any lower. And we're using the TSP (Team Switch Plate) to pull the pads back a bit more than normal so you'll only have ~15mm to tighten the cockpit. All that gets summed up to say "the medium is a hair too big". A better situation is this....
On a size small SLX with a short stem you're in the stock mounts so you can come back as much as 33mm and stretch out as much as 90mm - lots of room to move there. AND in terms of "pad elevation" AKA "drop" AKA "Pad Y" - I'm prescribing 30mm of spacers so you can go down 30mm or up 25mm. You're right in the sweet spot of a size small. That's the bike for you!
If you have ANY hesitation or questions get back to me here. AND, if you'd like me to call your fitter to discuss the fit you had done and the numbers you walked away with I'd be happy to do that as well. I'll do it in a very respectful manner. PM me if you want me to act on that.
Ian Murray http://www.TriathlonTrainingSeries.com
I'm all about athletes mastering triathlon
Twitter - @TriCoachIan