My vote would be:

1. Get a disc cover for your rear wheel. It's just such a budget friendly and cost effective upgrade.
2. Cockpit upgrade. Biased, but the Alpha One, like you mention, is the best option out there. This is has the obvious benefit of being faster and the less obvious one of allowing you to play with your position for potentially more comfort/additional aero benefits. EDIT: You may even be able to add a Delta cover if you go the alpha one route. Haven't seen one on an Argon before but I don't see a reason it wouldn't work. May even hide the front brake cable.
3. Go down to one bottle BTS. May not be possible if you can't rely fully on the G-endurance or whatever the on course nutrition is, but two bottles sticking up vertically like that are definitely adding some drag.

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Benjamin Deal - Professional - Instagram - TriRig - Lodi Cyclery
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I'm, still rocking an E-114 and Taupo is my 'local'. Did the full in 2008 as a tourist from Pommieland, then moved over in 2010. Hope we are able to host you soon, it's an amazing venue.

But, two words of warning. First the course is a really rough surface, and so one of the big issues I have is with my E-114 I'm locked on narrow tyres, which is of course pretty harsh after 4.5 hours. Second, the entire course is littered with bits that have fallen off bikes by the end - bottle cages, spare kits, a lifetime of CO2 cartridges that have come out of the screw in holders. I've lost bar end shifters and aero bars on training rides there too. So in terms of your setup, then consider that you want something that's fairly robustly mounted to withstand the vibrations. And finally, the volunteers at IMNZ are legendary. Really are. However, no matter how well prepped you are, taking on course nutrition is a lottery. One year (2013) they didn't stir it properly, so essentially you got water with slight hint of Horleys (the nutrition at the time). Hence lots of people bonked, I needed to swap to a plan b of taking coke from lap 2 of the bike as oppesed to lap 3 of the run. Was the only time I relied on the on course nutrition and it bit me. And although I'm not racing this year, then IMNZ has been, in my opinion, pretty poor in terms of athlete welfare the last two runnings (2019 and 2020) in terms of announcing the nutrition supplier. 2019 they moved to their own branded stuff, which wasn't available in New Zealand until mid January (for a March 1 race). And then changed the on course hydration 2 weeks before the race I found out I was allergic at about 10km of run). And last year they changed the suppliers of hyrdration and energy very late again.

My point being for a full, and especially your first, then if you can find the storage to have it all on the bike then you are setting yourself up for the best day. I run a dual behind the seat, the one on the frame and a torhans aero bottle (can't run a torpedo on the E-114 bars). Behind the seat are my tools in a half bottle and a pure water from aid station. Then in the frame is a bottle of 4x concentrated energy mix. Aero is drink at right mix. So that gives me 5 bottles worth of drink. I add the cocnetrate to teh front then top up with plain water from the aid station - if I want more water then I take a glug from that. Special needs has another bottle of concentrate in case I drop my main one on lap 1 (and some spare tubes/ co2) - otherwise I just ride past, but it's part of my Plan B.

(But I' still thinking of that E-119 disc. I'm getting old and 22mm tyres at 110psi for 180km of rough chipseal are becoming less fun with each lap of the sun).

I actually had my spare kit eject from my bike on the decent in Nice last year, so spent the last 30km of the bike just praying I didn't get a flat haha. I've actually replace the mount BTS and the new one allows them to be a little more tucked in behind the seat on an angle. Next time though I'm definitely taping my spare kit secure if I continue to store it BTS.

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Strava

Yep, I tape it in and that means I've got some tape with me for botch repairs too.