It's 6000 RPM on the unibody models as well. In either case the utility will not let you set the fan speed below the minimum or let you exceed the maximum. (so you don't overspin the fans) I just set it by feel; I let it stay on the default (2000 RPM) unless it gets hot, which is when I set it to 3250 RPM. If I'm going to be doing CPU/GPU intensive work I set the fans to 4500 RPM preemptively.