I recently switched back to SLI and although I wasn't satistisfied with the high GPU temperatures, like some of you I keep the side of my case open since I swap out graphics cards frequently.
With an SLI configuration using the GeForce GTX 280, I was able to knock of 13 °C (from 98 °C to 85 °C) in the Furmark Benchmark
at load using a quiet running 120mm fan! This was accomplished by affixing the 120mm fan to blow hot air away from the GPUs like so:
A 120mm fan is perfect for this type of application as it does a great job of pushing the heat generated from the graphics cards out of the case while running extremely quiet.
At idle the GPU temps are running at 50 °C / 49 °C with a default GPU fan speed of 40%. At 50% fan speed, temps drop to 48 °C / 47 °C and at 60%, temps were 45 °C / 43 °C. Room temperature during testing was 70 °F / 21.1 °C.