A 50x11 gear is actually bigger than a 53x12....
I run a 50/36 on my 2500 and 5200, and a 12-27 on the 5200 and an 11-26 on the 2500 (race bike). I think I spun out my 50x11 at around 50'ish mph....is that fast enough?
I would never go back to a "standard" crankset, even if I lived where it was completely flat.
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2016 Trek 520 (54cm) touring bike for sale - never ridden. Message me for photos/details.