Is everything compatible? (this is my first build last thing I need is to screw something up)
Is it overkill for what I need it for? should I downgrade the MoBo or RAM?
Is that a poweful enough PSU? Is it reliable?
I've read that the 955 runs warm, Do I need extra cooling? (I don't plan to OC)
Any other suggestions/comments?
Well everything looks good! The 5670 GPU is nice and should work well, but at 1920 x 1080 resolution, your probably going to have to turn settings on some/most newer games. If you want better settings than I'd suggest getting at least the 5770 GPU. The next jump up from there would be the 5850, but that is about double the price of a 5770 these days
No, your CPU heavy (from a gaming standpoint), but everything looks good to me If you playing games around the Warcraft 3 era, than even onboard GPU's will do. The 5670 is even a good dedicated GPU to have!! You should love it and should be able to play the latest games even, if you decide you want to try one out. You'll just have to adjust the settings for the best game play.
No you don't void the warranty on the CPU for OC'ing it. They unlocked the multiplier on the CPU, so you COULD OC it! You should be able to OC it to 3.6-3.8 gHz on stock settings, that is why I suggest getting that CPU.