the performance gain is significant enough to justify the extra 40 bucks. C2D has some advantages over Athlon x2 6400. but it depend to a large extent on what you use it for? for gaming, ocing, go with E8400,no doubt about it. but just for daily work and no intention to squeeze every last drop of performance out of it , 6400 is good choice or maybe AMD 5000+ is not bad. the extra money investing on other components does make sense.
Only the Paranoid Survive
T-T
~ ~ ~ ~