I mainly play Wow, but i play alot of steam games too, like Left for dead, coutner strike source, and warcraft 3 rarely, i dont know a whole lot about overclocking, but which would be better for what i do? help please...
Either CPU is fine although you will undoubtedly get slightly better performance from the tri core.
Some people enable the deactivate cores with certain motherboards essentially making the dual core 550 into a quad.Sometimes it works sometimes it doesn't.If you're lucky and get a good 550BE that works with all cores activated it's like almost getting a Phenom II X4 955 BE
LfD will benefit from the X3 but your older games, CS and WOW, will not.
Check out the price difference on Newegg, if you can afford the X3, buy that.
Macth it with an AM2+ MB and DDR2-800 for a cheaper option or AM3 MB and DDR3-1333 for a bit more.