Yeah, I can't offer a helping hand for how to upgrade. But yeah, the Go 7400 would be better than the X1400. Pretty much the same: it has a 64-bit memory interface with about 1.3 times the clock of the X1400, which has a 128-bit interface, so it almost makes up for it on terms of bandwidth. Not enough of a difference to notice anything, probably. The only big difference is that the Go 7400 has GDDR3, as opposed to the X1400's DDR.
7400 FTW!