To do Crossfire or SLI you would need a motherboard which has a pair of PCI-E 8X or 16X slots. Most P55 motherboards like the Asus only have a single PCI-E 2.0 16X slot and a single PCI-E 2.0 4X meaning they can do only do asymmetrical Crossfire which means a loss in performance. However,Crossfire is only for ATI or AMD cards and SLI for Nvidia cards.
The Phenom II X4 955BE is still a capable processor for gaming and is easy to overclock due to the unlocked multiplier. Both the Phenom II X6 1055T and Core i5 760 can also be overclocked. The Black Edition moniker only refers to an unlocked multiplier which makes overclocking easier but using the multiplier is not the only way to overclock a CPU though. However,overclocking is not guaranteed with any CPU and if you want to try and get a decent overclock with most processors an aftermarket heatsink would be a good investment
IMHO.
The Gigabyte motherboard I listed has both USB 3.0 and SATA 3.0 too. Unfortunately,the P55 motherboards are still extremely overpriced for the feature set they offer over the comparable AMD motherboards.
Also,if you have a Trust PSU it would be better to get a decent PSU from a well known company. Cheap PSUs are known to cause problems as the rated power is no where near what they can deliver with any degree of stability.
I would probably stick to your 9600GT as getting an SLI capable P55 motherboard is not cheap.
Once you have some more posts you can get free postage from Scan: