Thing is most of the regular forum guys are not that into extreme styles (me neither), so the answers will not be as great as asking for classic rock PUs.
I am no expert in the field but IŽll try to offer some info non the less.
The AM is very dry, super tight and middy. Does not really reliver the monster palm mutes you wish. Amazing for tech metal and some versions of modern rock, but not for you I guess (does handle low tunings very well though).
Take the AM make it fatter, more agressive and basecally put it on steroids and bathsalts and you got the Painkiller.
C-Bomb could work too, it is said to be very 90s metal though. Dunno if that is for you.
C-pig might also work, certainly will be monster. I would in my mind maybe have some reservations about it at such low tunings (too much bottom end), but I hear it works suprisingly well.
So I would guess Painkiller with the Pig being the runner up, but not too closely. But again, guess is the keyword.
You can also drop a mail to the BKP customer service and either Tim or Ben will give you a much better recomendation than I can.