I have almost the same stats as you, and I ride a 54cm Specialized, which has a 54.8cm top tube length. It is great for regular road riding, but it is too big for me to get the right fit with clip on aerobars for TTs. I'd definitely need to go down a size for aerobars, even if I got a TT-specific frame (which are often built with shorter top tubes for the size). If I could get my saddle far enough forward, I'd be positioned with my knees too far in front of the pedal axle. I do run a 110mm stem, but I wouldn't want to change stems just for TTs either. Plus, moving down to a 90mm stem would change the handling of the bike.