Originally Posted by Hida Yanra

For the new super-bikes, Tom D (founder of FIST fitting protocol) advocates getting the larger model, so that it can be run with as low in front as possible.
The low-in-front apparently more than cancels out the added size of the bike.

Now, not everyone would agree with that methodology, but that's probably what the FIST folks are going by.

If your bike is primarily for riding, and it works well for that, I'm unsure why you'd want a size that fits less well, just to improve your ability to throw a leg over it.
IMO, reach is a good bit more important as it is more likely to affect steering & balance on the bike. Lots of fast folks run their Shiv TT with a spacer stack, so there's less worrying on that end.
I'm assuming that you want to run all the equipment in the Shiv TT module (aerobars/stem/etc)... do you get multiple stem lengths & angles with the module?