Overclocking the xFSx 6950 2GB help/suggestions

Hey guys I'm new here and fairly new to computer building, I build my first tower last may and was looking to overclock my 6950.

http://www.newegg.com/Product/Product.aspx?Item=N82E168...

Thats the card I have and I bought a better GPU cooler the other day for $50. This is what it is.

http://www.newegg.com/Product/Product.aspx?Item=N82E168...

How far can I expect to be able to push the 6950? And to my knowledge (by me looking) I don't have a bios switch. So do I have any options there and should I even bother trying to go nuts with this card or just try to sell it for decent price online and buy one that has a bios switch or better clocking abilities. I have MSI afterburner unlocked to where you can change the voltage etc. I don't know, just give me your input I'm all ears. Appreciate it guys.