I usually underestimate how long I should roast veggies for. Plus being next to the bird, they will cook a little more slowly than if they were along in a pan, plus at a lower temp to begin with. I'd up it some, though you do have turkey resting and carving time to add on, so maybe an hour plus that is okay. IMO too the cooked veggies will hold fairly well, whereas being undercooked is not too great.
And yeah, cooking a roast or a bird at too high a temp is going to overcook the outside/outer parts before the inside is to temp. Though I do like the method I saw on Alton Brown's show, where he started the turkey off at 500* for half and hour, then lowered it to normal. The effect was to basically sear the turkey, to seal in as much juice as possible right off the bat. Though I also saw the opposite method on allrecipes for chicken, roasting it at something like 200* for something like 5 hours (don't know if it would work safely for something as big as a turkey).