as long as you're not on the threshold, generally you don't have to... as long as the cylinder is matched to range of barrel lengths, you don't have to do much hardcore calculating.
My research has noted that 6.03s perform much better than 6.01s
Though my upgrade philosophy is to correct the compression variance first... fix it so your gun shoots as close to the same fps as possible on every single shot. Your consistency in accuracy goes up as a result. Adding a longer barrel to that is the last thing to do.