Top tube length for the 56 is 55.7cm and 54.5 on the 54. As someone previously specified, only 1cm difference, really not much. How do you measure effective TT length?

I've had a bit more time to ride it and have made some tweaks that have gotten me a little more comfortable on the bike. (1) I nudged the saddle forward a quarter of an inch, the seatpost height feels great so left this untouched, (2) I moved the aero bar reach back about an inch or inch and a half which puts the pads a little higher up on my forearm and gets my elbows closer to a right angle, and (3) removed the 3 steering tube spacers to drop the stem although thinking about adding 1 back cause I'm starting to experience a numbness in my adult place that wasn't there when I had only dropped the stem 2 spacers. (Side note, also just ordered an ISM Adamo Race saddle to see if that will make a difference for my boys.)

All in all, the bike is starting to feel more comfortable as I'm beginning to dial it in, but it's not quite there yet. I think I'd like to get a shorter stem, even just a 90mm rather than the 100mm that's on there to get my arms closer to a 90 degree angle. It's probably around a 105 degree angle right now and I'm finding it's putting some strain on my arms, especially after a swim. Does anyone make 80mm stems? And just out curiosity, whats the effective stem length of your typical aerobars with integrated stem?