Man, haven't been to these forums in a while. But just building a new rig and faced a similar dilemma (the ol' Pentium D and 7800 GTX is in dire need of an update).
Decided to go with X4 965 myself (I was able to get 25% discount mind you, so at ~$150 CDN, it was a serious steal). Platform costs will undoubtedly be cheaper with the AMD platform (but I did have many headaches trying to find an appropriate motherboard. Trying to find a 790FX motherboard that supports the C3 965 out of the box was a huge pain so I just went with the vanilla 965 for compatibility's sake).
Nevertheless, if we're just comparing CPUs, then at the same price the i5 is better. Turbo boost pretty much guarantees that, it also OCs better if that's important to you. I'm assuming platform costs aren't important since you appear to be considering an i7, personally I think you're better off just saving the cash and just going with an i5.