AMD's have worse individual core processing power, and to my knowledge, no game will use more than 3 cores anyway so having six is useless (AC for example only uses one). Basically, intel's have stronger single-threaded performance and in my experience they also cool better.
No matter how good your graphics card is, your CPU can still be a bottleneck to performance, but it depends what you're looking for. I built my PC because I wanted to run skyrim on ultra settings when it came out, and thus I selected an i5 3570k over an AMD FX6300 since there was a 10-fps drop (ish) when using the AMD CPU rather than the Intel.
And finally, Haswell CPU's have the best architecture/design for games performance on the market atm, but even the old Sandy/Ivy bridge models are nice. I would always recommend an Intel over an AMD processor (even for people who don't game), but if it will put a massive dent in your budget then don't bother. If you're just looking to play AC with high FPS your whole system is overkill, not just the CPU.
EDIT: missed everything Waffles said, he's 100% right.
No matter how good your graphics card is, your CPU can still be a bottleneck to performance, but it depends what you're looking for. I built my PC because I wanted to run skyrim on ultra settings when it came out, and thus I selected an i5 3570k over an AMD FX6300 since there was a 10-fps drop (ish) when using the AMD CPU rather than the Intel.
And finally, Haswell CPU's have the best architecture/design for games performance on the market atm, but even the old Sandy/Ivy bridge models are nice. I would always recommend an Intel over an AMD processor (even for people who don't game), but if it will put a massive dent in your budget then don't bother. If you're just looking to play AC with high FPS your whole system is overkill, not just the CPU.
EDIT: missed everything Waffles said, he's 100% right.