Go 3600. Most LS engines really come alive at 3500. A buddy of mine ran a 3600 with stock cam for awhile just for gits and shiggles. It was damn quick too
I lost a pretty consistent 1 mpg when driving the same as before. I don't have stall yet but driveability is no different than stock. I have several buddies who DD cammed trucks with 3600-4k converters and driveability is no issue.