If your PC has more than 4g of ram or less, go with GB1. It will keep potential freezes/lockups/errors to a minimum.
If it is over that, and your CPU can handle 4 HB.exes running, do that. Also, if you happen to have 2 internal hard drives, run 2 of the bots off an install of wow on drive 1, run 2 of the bots off an install of wow on drive 2.
Better information pulling to the Wow.exe