that's exactly why I always say gates or turning down pots won't help you any.If you've ever played a clean passage, or sustained a clean sound on P90s, you'd hear the hum very obviously. The only real option is to simply change what you play when using a P90 guitar, and use something else for those more sensitive moments.
finally somebody who understands ...
and make no mistake, it gets worse as you increase gain, not better !
your only chance is to eliminate noise right at the PUs, and that's where it gets tricky.
limiting my playing is not an option, I'll rather use a more silent guitar instead - as unfortunate as this may be.