I’ve got a system that’s similar to yours, with key differences.
Similar: Same CPUs, 6GB RAM.
Different: G-SPEED ES RAID 5 (as media drive), 2x500GB RAID 0 (as boot drive [yes, I live dangerously]), Nvidia 8800 GT (way slower than your video card).
In short, you’ve got more RAM, and a faster video card, but I’ve got a substantially faster storage system. I wouldn’t call my FCPX experience as “silky smooth,” but it’s consistently smoother than what you describe. Are these issues while anything’s being rendered in the background?
And if anyone reading this has some insight (perhaps best for a new thread), would a change to a faster video card, such as a flashed GTX 285, be a significant change for me?