I have a 650, 550, 3 Square Deals, rockchucker, Lee classic turret, Frankford arms single stage and a Lyman Spar T for Blackpowder only. I use them all. The 650 is the workhorse for my 9 MM's and .45 ACP's. The 550 is for .223's, 30-06' for my pair of Garands, 41 Mag, 30 Carbine, 6.5 x 55 Sweede, 7.62x39, 30-30, 327 Fed. One SD is dedicated to .44 Spec, another to 38's and the last to 45 Colt and 454 Casull. If I ever get the Lee running properly I suppose I could take some of the load off the 550. The rockchucker is for load development and for small runs of anything that interests me. The Frankford single is made of aluminium and I pretty much use it just for decapping brass. I also have an ancient Lee Challenger that was my decapper until I got the Frankford (bad press in my mind--too loose) that I call the clanker. It does the job but protests constantly.
I had a burglary a while back and I just now replacing the 650. The new one arrived a few days ago and I am happily upgrading the dickens out of it. When I get done it will be a racehorse with power and speed.