If you're happy with spending the money on that (not criticising you or anything), then go for it.
Although, to be honest, I would downgrade the CPU. You have a SWEET motherboard, and can easily overclock a low-end Athlon to the speed of a high-end Athlon. Look, I can overclock a X2 3800 to 2.45GHz, overnight-dual-prime stable (incredibly stable) - faster than a 4800 at stock speeds. All without raising any voltages (and it's raising voltages that damages components).
You may as well go for a 4400X2. Same amount of cache, but cheaper.
Regarding the GPU, I would again say get the cheapest 7900GT you can find, and overclock it. Then theres no need to buy a higher-clocked card for more.