Check out Brian Enos's FAQ page for a lot of good info on the Dillon presses. He recommends the 550 if you plan to change calibers often. Also, the additional setups for the 650 are more expensive. But the 650 with a case feeder is certainly faster. I've been running the same 550 since around 1985, and I like the manual indexing and the ability to back up the process to check the powder charge or pull a problem round out of the production line. Check out the Square Deal B while you're at the factory. Some competitive shooters have one in each caliber, and they're pretty fast and Dillon-reliable. Good luck.