Allright, i just built my first rig this summer. I have An AMD x2 4200 (am2) on a gigabyte s5 590 SLI motherboard, with a BFG 7900gt OC Graphics card. The  GPU is being cooled by a Zalman VF-900. Does the fact that the card came pre-overclocked mean that i cant OC it any further? How much farther could it go and would it be worth it in the long run?

for the oc version, you are paying a premium for a stock7900gt that is guaranteed to OC
 
so there isnt much more headroom
 
the only reason to buy these OC versions are  
1 if you cant be bothered OC ing or
2 they have 3 years warranty

Well then i guess i made the right decision then, cuse the card actually comes w/a lifetime warranty