Which memory build would be faster?

Hi,
I'm thinking of upgrading the memory in my Gigabyte Mobo : GA-M61P-S3 from 4 x 1 gb dual channel DDR2 800 (PC2 6400)
If I upgrade, I'd get 2 x 2 gb of the same speed(to replace 2 of the 1 gb sticks), but I believe I'd no longer be in dual channel mode if the new memory doesnt have that feature correct?

So what's faster, 4 gig of dual channel memory or 6 gb of total memory single channel?

edit: I found another pair of dual channel 2 gb x 2 so...if I have 2 x 1gb dual channel and 2 x 2 gb dual channel I should retain dual channel mode correct?