Honestly I like a 550 for loading different calibers of pistol and rifle. That's easy for me to say because I don't have a 650 but the price of all of the conversion pieces to switch between calibers on a 650 is pretty high. Actually, the lady at Dillon, I think her name is Debby, recommended the 550 to me because of all the different calibers I load for. I especially like the fact that when I load for precision rifle, it's easy to individually trickle powder charges and then put them back in the press and continue with the process. Also, when I load bulk ammo I can still chunk out about 300 an hour and I go pretty slow. I'm not saying I wouldn't love a 650 set up solely for 9mm or .223 but my 550 rocks and toolheads, powder dies, and conversion kits are fairly cheap compared to the 650. Just make sure you factor in a toolhead and powder die for each caliber you want to load so you only set your dies up once. Oh, also order a few extra primer tubes so you don't have to constantly stop and refill the only one you've got. You'd be amazed how fast you go through a 100 primers.