I think the "swim" test isn't a bad idea for portage boot criteria ;)
Depending on water temp and wave conditions you might NOT have time to get your foot gear off if you can't at least dog paddle with them on? I changed my thoughts on footwear after reading Jimbo's story regarding the guy who's hip style boots almost drowned him!
Coming a shore with bare or stocking feet could be tough depending on the shore conditions.
I tested my PFD and shoes by wading out at my local lake and trying to swim parallel to the shore for a ways.
You want your PFD to fit well enough its not floating off you or hindering your swim stroke.
Better to find out in conditions you pick rather than the worse case scenario ;)