DKS is worth it for the performance optimizations alone. I tried Div2 when it was first released and found it awful - FPS bouncing like crazy, dropping below 20 for no reason. It was unplayable. Now, with the frame limiter off it doesn't drop below 120, though I set it to 60 and turned on vsync anyway.
Also, SLI really isn't necessary. I've noticed that DKS is mainly CPU-intensive as it only puts a 30% load on my 6950 and the temps never go past 50C. Witcher 2 and Dungeon Siege 3 put 80-90% load and temps can sore past 90C if I don't manually set the fan speed.
