Here are my 2 concerns:
1) The pro8200 is a factory refurb and only has a 90 day warranty. It does have 1080p though. Anyone have any experience with factory refurbished projectors?
2) The 710 HD is a light cannon that would do fine for an upcoming movie night where I will be projecting onto a white garage door (don't need opinions on that fact, I've done it before and it looks good to me). Do you think the pro 8200 would be bright enough for such an occasion?
The Pro8200 is also a light cannon, but the Epson 710hd is more of a light cannon. I own a refurb Pro8200 as a backup projector, 2500 hours on the lamp and no issues yet... I've had it about a year (I leave it on almost 24/7). I own other projectors as well.
I would assume it's bright enough for your setup, but cannot say for sure since I didn't see the room conditions, the screen size, etc... If you are projecting movies in a semi-dark room, I don't see how the Pro8200 wouldn't be bright enough.
The only downside to the Pro8200 refurbs are that they might not come with the latest firmware, but it's no big deal really other than the fact it can lose some color settings (only 3, they are easy to reset). The color is so accurate after some lamp wear it doesn't even need calibrated that much anyhow. It's one of the most accurate projectors ever made after lamp wear as far as calibration, it actually gets more accurate the more hours you put on the lamp, which is weird and different than most projectors. At first there is a RED tint, but the RED goes away after the lamp wears in (Lamps often naturally have a bit too much of RED or Green to them until they wear in).