RE: fastest SB revo???
Mayhem is right, everything counts. You are shaving off a very high percentage of weight when taking off 2lbs a truck. RWD will definitely help, I've done all of these trucks with my Savage, except I was lazy and left the diff inside the bulkhead cause it takes long to access them on the old Savages. Beware that breaking really sucks with only the rear, but it comes at the price of removing weight and rotating mass. You should definitely hit 50 with that setup.
Tom.