Hand polishing is an absolute pain in the butt and knackering, if I ever do it again I'll rent or buy a DA!
It's not any quicker with a DA, because then your more inclined to do it properly, and then it takes ages. You can hand polish a car in an hour or so just firing round it with the polish, then again to take it off. Once you get into the groove (the guy who valeted my Passat did the whole thing in 2 hours, including claybar and hand polish, as well as the interior). I just did my Golf with the DA, and that took 7 sweaty hours. That was wash, snow foam, wheels, tardis, DA polish, sealant and glass. Not even a wax over it. And it was only a Golf, so not exactly a big car. Anytime I have used my DA (which is obviously not often enough), it has always taken ages, because once you have it out, you might as well do it right (and I wasn't so bothered on everything below the bump strips either, so they didn't get hit quite as hard as above, plus, I only hit each panel once).