I bought a 450 in about '81 or so, upgraded it to auto primer and powder when Dillon came
out with them, around middle 80s, maybe '85 or '86, IIRC. Used that machine until around
the 2001 time frame or so, when I sold it and got a pair of 550s, easier to change calibers
with the toolheads. I have never used a 650 myself, but several friends have upgraded from
550s, and I have heard some issues with the primer feed system, which is, I believe, a disk
system, entirely different from the 450/550 linear system.
I rarely run more than an hour on a 550, and that usually gets me 400+ rounds. I find that
a nice, steady rate is about 15 min for 100 rds, plenty for my needs.
Bill