If you only do gaming, Phenom X4 is more than enough, if you do lots of video encoding, heavy workstation 3d rendering, F@H, Core i5 is the way to go.
http://www.legionhardware.com/document.php?id=869&p=23
The Phenom II X4 results were quite different to those recorded when testing with the Core i7 processors, though this was not necessarily a bad thing. When operating at lower clock speeds, the Phenom II X4 did not fair all that well, as we saw a sharp decline in performance. However when clocked at 3.0GHz and beyond, the Phenom II X4 really picked up the pace, and in many cases was able to outclass the Core i7.
In games such as Wolfenstein, Call of Duty: Modern Warfare 2, Tom Clancys H.A.W.X, BattleForge and Far Cry 2 the Phenom II X4 processors were actually faster when clocked up near 4GHz! This is quite amazing as out of the 9 games tested, the Phenom II X4 series was faster than the Core i7s in 5 of them. Although the margins were very limited, the Phenom II X4 was found to be faster, and had it just managed to match the Core i7 series with the Radeon HD 5970, we would have been impressed.
While the Phenom II X4 matched the Core i7 in Crysis Warhead, the only games where it failed was Company of Heroes Opposing Fronts, Left 4 Dead 2 and Batman Arkham Asylum. The Phenom II X4 was noticeably slower in these games, making the Core i7 the better choice here. Still, for the most part we found the Phenom II X4 to be every bit as good as the Core i7 processors when gaming with the new Radeon HD 5970.
Having said that, we recommend that AMD users looking at buying this powerful graphics card make sure that they have a Phenom II X4 processor that is clocked at 3.0GHz or greater. Most Phenom II X4 processors are capable of overclocking to 3.0GHz and beyond, while the more high-end options, such as the Phenom II X4 955 and 965 processors, come clocked at 3.2GHz and 3.4GHz respectively.
While we hardly expect there will be many users trying to pair a $600 US graphics card, such as the Radeon HD 5970, with a budget processor, it is nice to see that the sub-$200 US processors are up to the task. The Intel Core i7 920 proved to be more than powerful enough at $280 US, while the AMD Phenom II X4 955 will work just as well at $165 US, giving users plenty of great options.