My Sidi's are quite old. I believe they have chagned their lasts slightly since then. I tried on some Shimano 51's last year and they seemed to run just slightly longer than the Sidi's. I could probably be happy with a 50 in the Shimano. I haven't tried on Bont's, but, according to their fit chart and suggestion that you add approximately 4mm to your foot length, I would be a 51 in those as well. I pose a slight fit challenge in that my feet differ in length by about 5mm.
Vesteroid, can you wear a 15 Nike? I can't. They run too small for me. A 15 New Balance on the other hand is 'just' acceptable. If they did a 15 1/2 I'd be set.
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Birth Certificate, Passport, Marriage License Driver's License and Residency Permit all say I'm a Fred. I guess there's no denying it.