. At stock speed that E8200 is perhaps a little underpowered for that 4850 (...).
No, it's not.
A fast Core 2 Duo, will not even bottleneck the fastest GPUs around. If he had 2+ GPUs, then yes it would make a difference, but that could be mostly fixed by Overclocking the crap out of that CPU.
I assume it's a single GPU, so he can pair whatever GPU he wishes to that CPU and suffer no loss whatsoever.
To the OP: You're more than fine. Enjoy that 4850.