offshorefisher

I'm now running Powertech Bra 21p props on my twin Bravo 2xes behind Yanmar 6lps. Originally, I ran Al 23s, but went to 21s to keep the drives alive longer. Since x drives came out, I bumped up to the ss Powertechs with good success so far (1000+ hrs between failures). Because in my game a couple of knots means a lot, I am tempted to bump back up to Al 23s or Powertech ss 22s. How do you think these props compare in terms of loading the drives? I don't want to overload and cause failures, but if the Merc Al 23 and SS 21 Bras are comparable in drive loading, I could sure save with the extra three knots. I was considering the ss22 Brs as a compromise as it's a smaller diameter than the 21 Bras I'm using now. Thanks for any input.