Need more info. Single/multi gpu? x86/x64? What gpu(s) exactly? So far the only no-cpu-bug combos I found with my current mining boxes are single gpu setups. I havent found any reliable multi-gpu setups that have no cpu bug and ensure 99+% gpu activity during mining.
12.1 + 2.6 + single gpu + low-medium aggression = no cpu bug. (5830 @ 975/1200 AGG7 WORK64 VECTORS4 phatk2 phoenix, ~310mhash)
11.11 + 2.1 + single gpu + any aggression = no cpu bug (5830 @ 990/330 AGG12 WORK256 VECTORS phatk2 phoenix, 322.7mhash)
I think 11.6 + 2.1 + multi gpu = no cpu bug, but I had problems with my gpus not maintaining 100% gpu activity and my hash rate suffered.
Multi gpu, but second gpu is a mobo chip. HD5770 and internal chip HD4250 on motherboard. Windows 7 x64. I use 4250 for browsing, bd movies, games, etc, just to offload 5770. I don't have cpu bug with XP (32 or 64 bit) with both 5770(arrgession=12)/4250 active and 11.6/2.4 or 2.1 (same performance to me).
Cant get 2.1 to work on W7x64, more here. https://bitcointalk.org/index.php?topic=61078.0