Like Mike C pointed out, a great par 6 has yet to be made. Whether that's because they are pretty much used as gimmicks or because great designers fear they'd be seen that way and thus avoid them, I don't know, but there aren't many around. I'd have to give you points for gutsiness to use a par 6 as a closing hole, but it better be one hell of a hole to overcome the par 6 stigma. If an 18th hole doesn't work it can leave a bad taste in the mouth of a lot of people as they leave the course. Longer holes like that are also that much harder for poorer players (good way to pad the slope though, I guess) and having a lot of players end their day with a double digit hole isn't going to do any favors for word of mouth, even if it is the first great par 6.
750 sounds kind of short for a back tee measurement, that'd be a wedge to get an eagle chance for a guy like Tiger, and while most of us aren't quite that long, its certainly not going to be any great challenge to hit in three given two relatively solid shots to start out, or a trivial wedge to the green for the 4th for shorter hitters or those who fail to stay in the short grass.
Just thought to point out that it should be easy to calculate the USGA minimum for the hole. They say scratch players can hit 250, and thus a par 3 is up to 250. They must assume a second shot can go 220, thus a par 4 is up to 470. So add 220 more and you get 690 as the minimum for a par 6 by their standards. But I don't think there are very many 471 yard par 5s being developed anymore, for the back tees par 4s seem to go up to 500 these days, so that 750 is at the realistic minimum today, and won't age well if equipment advances continue unbated by the USGA.