If you want to save money, get an E2160, they seem to have very good overclocking potential at a low cost. If you can afford an E6550, then get that as it will give you good results also, and have the 4MB of L2 Cache instead of 1MB.
the 6050s have 4mb cache and 1333 fsb,
the 4000s have 2mb cache and 800fsb,
the 2100s have 1mb cache and 800fsb,
the 6300 has 2mb cache and 1066fsb.
if you're getting a good P35 MB, you'll be able to overclock any of them just fine. the 6550 will probably go the highest, and it has the most cache, so should be the best performer.
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They call me crazy for yelling, alone in my room, at the computer screen. They just don't understand the game.