The usage of a particular CPU is up to the application and the OS. Different OS tasks can be assigned to individual CPU's, and applications can do that as well. To load both of your processors at 100% means you are CPU bound, hard to imagine with any recent processor for an extended period of time? On my Intel i7-920 these, 1 and 2, are the most frequently used, but I can only recall a few instances where even 1 CPU hits 100%? Right now, as I type this I'm running Pinnacle's Studio 12 creating (authoring) a 2 hour DVD, the program is working its way through the captured AVI file and producing and writing DVD tracks. My CPU total is fluctuating between 10 and 14% overall, and CPU's 1, 3, 6, and 8 appear active with the first 3 around 30 to 35% and the last 10 to 20%. The other CPU's have hardly no activity. RAM (I have 8GB's) is around 35% used.
Since you are on W7, go HERE and pick up the first gadget, it will show the CPU's percentage all the time. It doesn't seem to place any load on my system?
At this point, I'd suggest disabling ALL A/V's and firewalls. Worried about being attacked, pull the Internet connection. I'd suspect one of these is either scanning or polling something rapidly.