dont quote me
wireless G = 54mb/s
wireless N = 108 / 150 / 300mb's + greater range than g
so basicaly even if you had the 50mbit line you would be fine with G and still get your full connection speed.
N is only good for futureproof, or if your pc is going to be further away.
PCI wireless cards can have there signal blocked by the actual case, so be aware of this. a lot of people go for usb on an extension usb lead, so they can move it around for optimum signal. but its your choice with what you go with in the end.