I've asked around, apparently, for a mining rig there is no benefit of one over the other.
But if you look to the future, Device Drivers for 34 bit will become less available.
It lookse like the world is going to 64 bit, not because it needs to, but because it can.
sweet, thanks! Waiting for 50 USB's today, want to hook them up to a little notebook so hopefully it meets the other hardware requirements as well