A custom geared set of aero rings from Fiber-Lyte would do the trick. I find gearing to be just as important as tyres. I use the Vittoria Evo-Tri and it has a much better puncture resistance than the chrono. The first generations of the Evo-tri were under 200 grams and very fast. I still have a couple sets I use for races. I also used the aero Fiber-lyte rings and was pleased with their performance. I used the Felt DA through three different models and found tapered ti bolts, shortened seat post, stem face plate swap, ceramic bearings(headset hard to find) brake pad holders, arm cups and pad swaps and housing were the best ways to deal with the integrated frameset. Good luck with the training and preparation.

i believe the main (only?) difference between the evo triathlon and evo chrono is that the triathlon version uses the butyl tube. this is so one can pump up the tires the night before the event and leave it in the transition area without the tire losing significant pressure. the chrono, with the latex tube, is faster though.

Also changing rings will change the SRM calibration, which I personally wouldn't want to deal with mentally speaking.

The London course is mostly on Brand's Hatch - which is a lumpy race circuit (think they used to hold the F1 there, now used for motorbike racing). Wind conditions likely to be variable (but it's a twisty course so it's gonna hit from all angles).