I know this may not help much, because I don't have personal experience with those particular model pickups but I think you would be VERY happy with either choice. I'd probably go with the Z90 but that's just because I went throught the same thing a while back and compared the same pickups as well. The Z90 just really floated my boat at that time.
You've certainly got the right guitar for it. Just personal opinion, but you can't beat P-90 style p/ups in a mahogany body. I have a Brian Moore C45 and the tone is plain gorgeous. I also have a PRS with P-90s (probably the same exact model) but it has a maple top and for some reason it's just not the same.
As far as the brands you're looking at I think they are both very high quality and have a lot of believers out there. I have a Rio Grande Tallboy Quinto set in a G&L ASAT and it sounds fantastic. A little noisier than I'd like but that's really only noticeable when you're by yourself in your quiet bedroom. Get some other musicians around and you can't hardly hear it. I'm going to put a Harmonic Design Strat-sized P-90 in another guitar but that hasn't happened yet so I can't comment on their quality, noise-level, tone, etc.
Anyway, get the Z90 (or Bastard) - it'll transform that guitar.