Another factor is the thickness/toughness of you whiskers. There are folks who will argue that hair thickness makes no difference. I don't agree.
Hair (which is what your whiskers are) can range in size from 20-200 microns. The thinner the hair, the longer your blade will work without needing to be refreshed. You'll have to take the time to learn your razors and your beard.
When I use multi-blade razors they start to pull after 5 shaves. I have friends that can use them for a month with no pulling.
Hope that helps a bit.