Yah, the problem is that i dont know, cause i dont have my monitor yet..
Monitor meaning only one? well unless you are planning to get a 2560x1600 (and even then it probably won't matter) the memory bandwidth and vram amount of the 670 won't be an issue. But when you get into the 5760x1080 + resolution is when bandwidth and vram can and will come into play on some games.
For a single 1080p or 1200p monitor I would go with the 670, anything higher get a 7970 or 7970 crossfire.