I've got the Oki C931 for doing envelopes and so far we've been happy with it. Here is what I've noticed:
1) Input tray only holds about 15 envelopes to reliably print straight.
2) Color looks good
3) Minimal creasing (so far)
4) When the drums say "Replace me" that's it. They're done. No more sticking it back in for a few more impressions. The machine is absolutely done and will not function without another drum.
5) Just got 38,000 impressions out of my black drum, and that was with mostly envelopes. If there's a way to reset the drums, I haven't found it, but I haven't looked either.
6) Straight Shooter has an envelope feeder for my printer, and mine should be here next week!
7) This Oki is WAY more tolerant of environmental changes than the previous machines (9800, 9650, etc.)
I wish I could reset the drums, because I really don't think mine is dead after printing 38,000 envelopes. If anyone knows a way, chime in!
For me, there's more good than bad with this printer, so I will stick with it, even though I don't seem to get as far with supplies as I would like.
Oki wanted something like $25k for their printer with feeder. I've got $10k into my printer, straight shooter feeder, and 6' long conveyor.
I'll report back after I get my feeder up and going and let people know well it works.