The first step in CPU spikes is to use something more advanced than taskman. Process Explorer is a must. If it is a device driver (the most likely cause although an AV is an other possibility), Process Explorer should show hardware interrupts spiking. It's possible to go further in Process Explorer and explore the hardware interrupts, but I think you're better off using your time to disable all non essential hardware and trying that. I'd say go to integrated but SB-E doesn't have that.
Other thing to do is to install a 2nd copy of Windows and see if that works (in which case it's a driver / program on your original Windows). Anyway these are good starting steps - where to go from here depends on what you find.
As an aside, I think some people can be under the mistaken belief that because they went out and bought the most expensive of everything that their computer will be trouble free: I think that tons of high end stuff is more likely to have the opposite effect actually. If you're going to spend £1000s you really either need to know exactly what you're building or go to boutique / consultant who does. But aside from bragging rights I cannot see the use of quad SLI.