I think that for a cover crop, most any variety adapted to the northern climates would work fine. Aroostook, Muskateer, Frederick, Puma, Maton II, and Oklon are all rated as above average for overwintering. I’d probably seed them around 1.25-1.5″ deep, and don’t go much deeper than 2″. I’d probably use a seeding rate of 60-120# per acre, and I’d be getting it in ASAP this time of year. Rye will germinate at 34 degrees F, but you might not get much winter growth before it goes into hibernation. If you’re feeling adventuresome, you might also put in 2#/acre of hairy vetch to go along with the rye, they complement each other pretty well, and the vetch will fix significant amounts of nitrogen if you let it grow to flowering. Good luck!