I was just curious as to whether or not upgrading my GPU from a 9800GX2 to a 5870 would be a worth while investment? The reason I ask is that a very good friend of mine said that my systems CPU a core 2 quad Q9300 at stock would struggle to keep up, do you share his opinion?
depends what resolution you play at and also what games you play, say for example you play at 1280 x 1024 or you play a game that only uses 2 or less cores then yes there will be a CPU bottleneck.
However if you play at 1920 x 1080 or above then the bottleneck is likely to move towards the graphics card (depending on what game you play)
So basically a Q9300 at stock isnt that fast, but it is a quad core. So if your playing a game that uses all cores then your be alright, if not then I'd recommend you overclock that Q9300 as much as you can.
I think your friend is right in that your Q9300 is likely to be the bottleneck in most games. Doesn't mean to say that you won't get playable framerates though