1) You should be fine running that mem at 667.
2) Don't worry about that. An e6600 is plenty CPU for current games and for pairing with that 9800GTX. Crank the eye candy (FSAA/AF) at any decent resolution with maximum details in recent games, and most of the time the 9800GTX will be the limiting factor.
edit: Check on the PSU though, a generic 550W may not have enough 12v power for a 9800GTX.