In lightly threaded applications not much difference would be noticed between the 965 & the E8600 as Phenom II and Core2 architectures IPC were pretty much on par with one another. Personally I would lean towards the 965 as more applications are being coded to make use of more than 2 cores where the 965 will have a sizeable performance advantage.
Well, I upgraded from a E6700 to a 965, and the difference is huge. Heck, my FPS in Skyrim practically doubled, the immense stuttering I had in games stopped, and don't get me started on multithreaded programs; Easily less than half the time is needed to do stuff.
World Machine 2 is so awesome now.