No, but with a $300 budget total, and him saying his primary concern is gaming, the video card is the way to go.
Now, if he comes across more money, by all means, buy a better cpu. But, since his board already supports quads, there is no sense in going AMD for him. Phenom II isn't any better than Yorkfield. They are virtually the same clock for clock, so why would you go thru the extra expense of a new mobo and new ram when what he has already supports the Yorkfields?
If he were going to go thru the expense of upgrading his mobo and ram, he might as well wait until he can afford to go with 1366 or 1156 at least. At least then his money would be spent on a cpu that is faster than both Yorkfield and Phenom II clock for clock.
Only those with systems that can't take Yorkfield, and require a full upgrade to move forward, would benefit from Phenom II. (Or those that just like to tinker with a lot of different hardware, or just want to build from scratch)