Of course, good idea Logan. OP, waste as much money as possible, because SLi is the best
You do realize, Logan, that a 15% gain in framerate is the threshold of being able to notice it? And in the vast majority of games that don't already pull over 60FPS on the 4870 only show about a 15% increase in framerate between the 4870 and GTX 460? If you've got something like a 4870, the smallest upgrade that will really make a difference is going to be something like the GTX 470. Even upgrading to a 5850 would be pretty lackluster.
The OP is looking for a DX11 card. Now I'm sure you'll agree that the GTX460 compared to the 5770, the first card the OP concidered is a NO CONTEST, GTX460 hands down. That leaves the next option being a 5830, something the GTX460 regularly beats. Now we are to the 5850 which wins most benches, I'll admit, but still loses in key DX11 based benches. And when you can spend 4-450 for 2 GTX460s and get better performance than 2x 5850s, yes SLI is the best. And sadly, no matter how many times I've provided links to prove it, you still deny it SLI as an option.
Case in point. Say the OP wants to go Tri Monitor, sure he could spend 350-400 for a 5870 and do it with a single card, or he could spend 4-450 for 2x GTX460s and get FAR better performance in the SAME scenerio.