If your board is oem dell, hp, etc. get the 8200 which is newer. If you want to overclock and your board permits it, get the q6600. If you're not sure about your board, try downloading the motherboard manual off the manufacturer's website. If your board isn't listed, chances are it's oem and has no overclocking options in the bios.
Performance is mostly the same, so unless your worried about overclocking just get whatever is cheaper.
+1,the performance of them is pretty much the same,and both OC good,go for the one which is cheaper but if you get the Q6600 make sure you get the G0 version which is better for OC'ng
------------------------------Q6600@3.4+ TT V1 Cooler,SAPPHIRE HD 4870X2,ASUS MAXIMUS FORMULA,4GB OCZ DDR2 800,LG W2452V 1920x1200
Reply to Maziar
If this is for a prebuilt, make sure to check with the manufacture that a CPU upgrade is possible for the bios. Just cuz the chipset on the mobo can handle it doesn't mean the bios will allow an upgrade like that. If this is aftermarket, you have enough info above.