Cost in mind, I would go the 3800+ route as you save a great deal on Mobo etc. expense.
i second that get the x2 3800+
although i would if you had the cash get the core 2 duo but seeing as you dont well get the x2 3800+ and overclock it loads, bear in mind a 3ghz x2 3800+ cannot beat a core 2 duo e6300 overclocked to around 2.4-2.6 ghz. so what? what if you get the core 2 duo and bad ram you cant overclock to high so its pointless speculating what speed your gonna get you might be able to reach these speeds with el cheapo ram but you might not. get the x2, a good watercooling system and then overclock, get a GL