Totally forgot about that particular card :lol:
Personally, I would just get the 670 due to it's huge performance gap. The 570 is a nice card as well, but I just don't see how it would be able to push three monitors at a relatively high setting considering it's VRAM.
Plus, with the left over $100 you have (considering you get the 670), you can save that up and put it towards your fund for two more monitors in the future for surround