I've been using PLCE for airsoft, cadets, and all that jazz for a good 4 years now, after spending 6 days in the field, on the most exausting junior leadership course ive ever been on, you dont even notice the webbing.
If its fitted properly, and not overladen, it shouldnt hurt at all.
Now, carrying an LSW, 300 rounds, a PRC 350 (a fat radio for anyone not military orientated, allmost 4Kg+2 spare batteries, = 6kg) and full combat gear, THAT is tiring! It was an endurance course though, so
Ive had bad experiances with assult vests, tbh, i cant stand the damn things, they dont have