Multi GPU...is there any point?

I am building a new desktop in September and I'm getting the new GTX590 as well as the i7 Extreme and Asus Rampage III Extreme, along with 8GB Corsair Dominator RAM. I plan to buy another 16GB RAM later, but I was considering getting a second GTX590. I'm more into production scale work, using Premiere Pro, After Effects, and Photoshop most often. Now I know from experience that with After Effects, I can actually run out of available VRAM with less than 30 seconds worth of footage, so the additional 3GB would be really helpful, but what other performance gains could I see from a second (SLI) GTX590?