For best performance, you should have between 1x and 2x as much VM as you have physical memory, as a general rule... at least for single-user setups. The automatic setting is also dynamic; that is not good for performance because it tends to fragment the drive and along with it, the VM file. You're generally better off using a fixed size VM file, by configuring it on a freshly defragmented hard disk or partition. That way it will remain contiguous, so you do not incur the extra overhead caused by having the paging file fragmented.