This thread has been inactive for five years. (Zombie Thread)
That said, are you able to test-ride both bikes?
My swb V-Rex is a candidate for heel strike but it has never been a problem. You learn how to deal with it/avoid it. Not sure how much of a problem heel strike on a Giro 20 is compared to a V-Rex. Plus, my shoe size is only 10.5.
Dual big wheels on the Giro 26 will make for a more aero position and will roll over imperfect surfaces better than small/big wheels on the 20.
Ideal situation is to ride both bikes to see which you like best.
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Bacchetta Giro A20, RANS V-Rex, RANS Screamer