4X AGP is the speed that the card and slot use. I don't remember how much this is, but the higher the speed, the faster it will be. but even if you were to get faster on either the card or the mobo, it doesn't mean that you will automatically get that kind of speed. Ex. my card is a 2X AGP on a mobo that supports 2X. If i get a 4X card, i would only be able to run it at 2X. Conversly, if i get a 4X mobo, but use the 2X card, i will still only be able to run at 2X.