To determine the graphics horsepower that you require, we really should know the quantity and size of the displays that you are planning on using. Are you planning on using a single 1920x1200 display? If so, a single GTX660Ti will probably suit your needs. Are you planning on dropping a grand on a 30" Dell IPS display? IF so, a single GTX680 should fit the bill. Or, rather, are you planning on 3x 24" displays, for a total area of 5760x1200. Because if this is the case, you'll probably need SLI GTX680/670.
Then again, have you considered Radeon cards? If you're only running a single monitor, the 7950 will have enough power for you. It typically slots in between a 660Ti and a 670, and guess what? MSI manufactures one:
MSI Radeon HD7950 Twin Frozr III
As a bonus, you get 3 free games. And these aren't crappy titles, either, but rather full blown, A-list games: Far Cry 3, Hitman Absolution, and Sleeping Dogs.
At least, that's what Linus Tech Tips tells me...