I'll put in another vote for the 5550B. It's my favorite Dillon.

1) It has a much wider range of caliber options than the 650
2) caliber conversion kits are less expensive than the 650
3) The 550 is manually indexed, and that gives you much greater control over what is happening on the shell plate. If something doesn't go right it's much easier to detect and fix. The set up is much quicker than on the 650, and the non auto indexed operation lets you run the press as a single stage press, a turret press, or as a progressive press.
4) the 650 does have a speed advantage but as others have noted 300 rounds per hour is easy to achieve on a 550, and 400 rounds per hour is do-able if you've got good dexterity and 4 primer tubes, even without a case feeder.

I've loaded at least 10,000 rounds (and closer to 20,000 on average) per year for the last 15 years with my Dillon 550 and I've still not worn anything out on it. I have had to tweak the primer feed a time or two to remove burrs that occurred after about 50,000 rounds, and snug up a screw now and then. I also replaced the cotter pin on the primer chute. I replaced it with a convenient paper clip that I straightened, and it's worked great for about 30,000 rounds or so, so I'm not in a big hurry to replace it.

Now, to be fair that round count is spread over 8 different powder measures and about 15 tool heads, and a dozen or so shell plates, and the rounds are split about evenly between the large and small primer feeds, so it primarily refers to the press itself.

If you keep a 550B reasonably clean, lubricate it now and then, and don't force anything that feels funny, it'll last longer than you will.