Originally Posted by
thisisbenji
I would disregard seat tube length, I would only consider horizontal top tube length. My Specialized Crux has a 52cm seat tube, and my Allez has a 49cm seat tube. Yet both have 53.7cm top tubes and fit perfect. If your already running a 90mm stem on a 54.5cm top tube I wouldn't get something with anything longer.
If your current ride has you on a 90 mm stem, the shorter stem (70mm) you would need on the bigger bike will compromise handling. I prefer stems in the 110-130 mm range with normal trail for neutral handling.