Onyx and GURPS

I continue to work on Onyx, my embryonic medieval urban fantasy campaign setting. While I am wanting it to be as simple and as systems neutral as possible, I am thinking that, when it is my turn to be GM for our Monday night gaming group, I will use Onyx as my setting and GURPS as my system. While a d20 medieval urban fantasy campaign is doable, I don't see it as the best match of setting and system. Fate would be good match of setting and system, but I am not sure how Fate would fly with my fellow players.

I am thinking of doing a heist-based sort of campaign: Fantasy + Constantinople + Oceans 11. I think it would be a blast with GURPS.