I do not know about a V5, but I have a Radeon 32MB DDR in my Celeron 300A. For Quake 3, I get ~42 fps @ 800x600 in 32 bit. o/c the 300A to 450 puts me at ~48 fps @ 800x600 in 32 bit. While not great, it is playable.
Next up for me is a CPU upgrade. Flight sims need a lot of CPU horsepower, and that is my favorite game.
In short, both you and I are CPU limited.