i'm running standard ford 071's
at 400 bhp with no prob
change them every couple months
no prob with them but they're only a tenner a set on ebay so might as well
mates got a 550bhp escort(pink 1 in sig) same plugs, no prob
other 1(black 1 in sig) is over 600bhp, again same plugs with no probs
just gapped right down, keep them fresh every couple of months
and you'll have no probs