John, I have the same mods done to my bike and i recently bought another 5-gallon drum of U-2. I haven't had the chance to ride long term on the new motor but i can tell you that i did not make any jetting changes when i switched from c-12 to U2 with my stock motor and there was no problem with detonation. Now, with the increased compression and race fuel specific porting, I'm not so sure but i can't see there being that much of a difference. If you want to play it safe just go up one on the main jet from your C-12 setting. I think mixing C-12 with the U-2 would take away from the potential increase in power that you would get from running it straight up. This is what I'm running for jets right now for C-12.
380 main
76 needle in second pos
30 pilot
S-8 nozzle
2 1/2 turns a.s.
v- force m/t
eric gorr mo-better porting
fmf fatty pipe and silencer
motul 800t @ 32:1
I have started my bike and ran it on the stand with straigt U-2. ( it was too cold to take it out of the garage) I know that throttle respose was better and that the smell of U2 exhaust carried through my house like there was a 747 on the bike stand. Needless to say that I'm the only one that enjoyed it. Hopefully Eric or Rich will chime in with some more definative answers.