the grey knights in power armor arnt that tough, they need numbers.
BUT, bet no one has anything bad to say about the terminators eh? One day my friends brother desided to start imperial guard, and was talking about how tought they are because he doesnt realize the 'fodder' factor required in IG. so i put one terminator (56 pts) against two units of regulars. he finally won, but look how badly out numbered he had to be to lose.
and another time i played with my brother using the enormous chaos army. He blood raged a FULL squad of khorne berzerkers (20) against about five grey knight terms. a few high piched bloody squeks later my unit carved right thu them with one loss.
mean while my nine power armor knights got blown away by two squads of havocs full of lascannons, that just wasnt fair, they didnt even have cover.