Bieng from the north country of NY, I prefer a larger, 9x12 or 10x10 tarp. The winds in a storm can drive rain under a 36" tarp for 36" easily. Even an A frame with one end mounted to the ground can be a challenge to stay dry, sometimes.
I figure the first 1-2 feet (next to the ground) is basically unusable for sleeping. It is too low for anything except gear storage, even with a stick poked up under it. For the next 7 feet, you ar least te sleeping under it. For the next foot or two, is clearence for rain spatter. In wind & rain, the extra width means you sleep diagnal, giving the requisite 3' of clearance. The width means you can fold up your bag, pad and pack under you as a seat and also cook breakfast in bad weather. Packing gear, and loading the pack is easy, except for the tarp. Last thing, the stakes and tarp are roled up and put in your pack's front pouch, ready to go.
In dryer areas you don't need anything like that. I suspect half those sizes will work. But for a week out in the ADK's, I expect two days of rain, maybe three or four. (I have been out for 17 days straight of rain every day.) But rain rarely lasts more than an hour or so. It is miserable to get up wet with your bag half soaked, though.