in the latest review here on Techspot of Phenom 9850, there were both e8400 and q6600 paired side to side...
as for the gaming, I take Crysis as the measure of all things when it comes to the future, and Quad is much better than the Duo, so I think that tells something, if a game is optimised for multithreading, which all of the future games should be, than it is quite clear which to take...
But I have a doubt, I asked in store for the stepping of Q6600 and they don't know it, so I'm afraid, if I buy the B3 one, in another post, I've seen that KO fixes some 40 bugs whic B3 had, so would it be too troublesome to have a B3 stepping Q6600?
if you have money and it is avalible, go for Q9450, you can't go wrong, it's quad and it's the latest technology availible.