My board is designed to handle a much higher load than the GumStix expansion boards, so it requires 7 to16.8V input, has a 6A 5V switching regulator to handle all sorts of fun stuff on the 7 USB ports, and a 1.5A 3.3V switching regulator for the 3.3V components including the GumStix.  I have not observed any spikes over 3.3V on the regulator, plus the TPS chip on the Overo is rated for 4.4V, with spikes up to 5.4V, so none of this makes much sense.