Full spec is below.
The whole system is due changing to be honest, it's a bit old now. For example the temperature sensor on the CPU stopped working (however I know it's safe) and there's a couple of other things I'm not happy with (like AMD's Catalyst Control Centre software!). I really do like Win7 though.
ABIT IX48-GT3 Socket 775
Intel Core2Quad Q9400 (2.66Ghz) (2×3 MB L2, 1333 MHz FSB, 95W TDP)
8Gb Corsair TwinX DDR3 1333
XFX ATI Radeon HD 5870 1024
SATA hard drives
SATA (Lightscribe) burner
Win7 Ultimate 64-bit
Triple Monitor EyeFinity setup
If your happy I wouldn't upgrade. Look back into it at the end of the year when the AMD 8970's come out. Also its getting close to you needing a CPU / Motherboard upgrade. May think about that this summer when Intel's Haswell comes out.
If you plan on gaming at all and use EyeFinity its time to upgrade. I had a 5850 and LOVED it, probably my favorite video card out of the 12 or more that I've owned over the years. The 58** series were great cards but they are getting past there prime. My card was good enough that I skipped the 6*** series of cards, but last year I upgraded to a 7950 and got nearly double the performance of my 5850. If you dont game then there is no need to upgrade, but if you want to play current games on a 3 screen setup, 1 gig of ram doesnt cut it anymore and you'll see a SUBSTANTIAL gain in power going with a 7950 or 7970. You'll also be able to add another monitor like i did since each card supports 4 screens now instead of 3 like on the 5 series.
Overclock that CPU if you can - it's still decent. And an HD 7970 would be your best bet for High settings on 3 monitors. What games do you play?
I have tried 'clocking the CPU but it's highly unstable and has a very small window of settings that works. I'm sure I abandoned overclocking as it was unreliable anyway.
I play the likes of Battlefield 3 across the 3 screens although I do have to turn some options down to get a compromise on frame rate.
May think about that this summer when Intel's Haswell comes out.
Not heard of Haswell, though I do have the time to wait. However it's going to be like everything else - high initial price so I'm not sure I'm that bothered.
If you plan on gaming at all and use EyeFinity its time to upgrade.
I'm talking to a builder at the moment about options. I have about a grand to spend on it so I'll see what they come back with.