You might notice a more frames per second with the $420 but the $370 is a really good deal for a 670. That is probably the best value out of all your options right now. I would go with the $370 670 or the 660ti.
I would go with the 660 Ti and save some money, I have seen much reviews and I think the difference 660 Ti and the 670 is not very substantial, except in higher settings. Max about 20% slower. But, the 660 Ti can be bought $100 less.
EDIT: Just found a 7970 for $420, with a 12% discount? maybe you should also take a loot at this? It trade blows with 680 so it could be a good option too.
well that deal is over.. but im probably just gonna save up money and in a couple months, purchase a 670. that way i get to compare it to the 660s.. im really diggin that GIGABYTE cooler. but if MSI ever did a 670 twin frozr thatd be something to get.