It depends on the terrain:
On mud or non-rocky terrain 4.5-5 psi (if too muddy even less)
If rocky terrain that could damage a rim then I go up to 8psi
I don't go any higher because of discomfort or because if any higher a sharp rock is more prone to cutting my tire I would think.
I find it to have very predictable slide characteristics with a lot of tires I've used in the past with these pressures, assuming they're 20" tires in the rear and 21" up front. The 22" rear razors required a little more pressure, while the 23" fronts required a little less. Just personal preference.