No need to worry about the SB. P45 is the way to go if you want a good board for you Q6600. Asus seems nice, there's an entire thread devoted to Asus P45's here:
http://forums.techpowerup.com/showthread.php?t=89468
G35 is older and hasonboard graphics
P35 is older
G45 hasonboard graphics and replaced the G35's
P45 replaced the P35