What apps or you speaking of?
First thing, just speaking on terms of a single GPU, that Phenom II, especially at that clock, should not bottleneck your 6850. I assume you have a 890 or 990 chipset, and they are pretty damn fast and play well with CPU - GPU combinations. My 1045t with a 6850 on an 890 chipset ran very well together, although it seemed there was a slight bottleneck at stock clocks. Right now, I have a FX-6100 @ 3.9 (on stock air) with a HD 6850, and they work VERY well together. I definitely run CIV 5 better, and by that I mean awesome, and that is super CPU intensive, so you should have no problems with your current set-up. Don't know how much of a difference the chipset would make for you in that regards, but the 990 was made for the 6XXX and 7XXX GPUs.
Second, I ask what apps, because some make much better use of you six cores than others. Even the good ones rarely access more than four, but most CPU intensive software is pretty good about CPU utilization.
Just a note though, something I don't see mentioned a lot in these forums, one of the best performance upgrades you can have is a second Hard Disk. That would greatly help you in the realm of CPU intensive apps, which are generally ram intensive. Allows your computer to read and write to page file at the same time without waiting really helps overall performance on the system level, and makes windows a lot happier, you just have to make sure you have pagefiles on both disk.
Lastly, you have two 6850s man, I know there are much more powerful enthusiast cards, but the 256 bit processors are no joke man ( they are 1.5 TFLOP chips, the first 1.5 TFLOP machine on the planet was in 1996 at the Sandia National Laboratory, and it was HUGE, so that thing in the back of your machine is as powerful as the most powerful massively parrelled computer in 96), so your not going to find a cheap processor that can keep up with 2 of them. I was thinking about getting a second 6850 for my 6100, but I know that on CPU intensive things, I can expect performance close to what I have now. Wouldn't really call that bottleneck though, it's just the limit of your processor.