After some investigation I've found the multi-gpu graphics cards dont perform so well in Arma 2. So here's my current thoughts:
CPU upgrade to Q9550 (Everyone here seems to agree that Q9650 isn't worth it?)
GPU upgrade to GTX 285 2GB
But I'm not too sure about the 2GB version of the 285... It's an extra $85 AUD ($67 USD) more than the 1GB version, will it be worth it?
And if not the 2GB 285, should I consider the very cheap ATI 4890, which seems to benchmark around the same as the faster GPUs in Arma 2 when the cpu becomes the bottleneck... Any suggestions?
edit:
I just ordered a Track IR Ultra so I already feel sick about how much money I've spent, but I do look forward to the most awesome gaming experience ever ;)