I ride a 56cm Cannondale Six13, fits me like a glove. I'm looking at a used 54cm Slice Six13 style TT bike. In the shop the 54cm TT bikes from Cervelo and Cdale really did seem about right, but it's hard to know since I've not really had the experience I have on a road bike. I may just buy this 54cm bike used (the price is certainly right) and see if I can get it to fit. If not I can re-sell it. I can buy this bike for $2200 with cheesy wheels. The new ones with Zipps retail for $5500, even with a discount, after tax I'd be laying out close to $5K.
No wonder so much bike schwag gets purchased on eBay.
I'm 5'11", longish legs, short torso. The Cdale TT bike has a short 53.5cm top tube. But that might not matter so much on a TT bike. My concern would be getting the handlebars high enough to get comfy on the bike given the small frame size.
What are the odds this sizing will work out for me? Anybody want to hazard a guess based on all that? I'd bet it would work...