Crank, you never did sound defensive.....just a guy wanting an explanation.
I don't know that you need to purchase multiple powders. You can narrow it down some by getting a little data from Quickload, if Chev wants to provide it, and then go from there. The slow end of suitable powders would be found where 100 percent or better loading density starts dropping off in pressure below your planned peak. Say, where you couldn't get 15,000 psi any more, or whatever your planned peak psi is. Since blowback movement of the bolt is proportional to the weight and velocity of your bullet, as opposed to that of your original rimfire the gun was intended for, maybe it wouldn't be such a bad idea to avoid what is possible and go for what is more prudent in terms of safety and not overdriving the gun.
Excessive breech opening is to be avoided, as is excessive bolt velocity. I would think that 1100 fps would be plenty with a 50 grain bullet and really cannot see where more speed would help with the advantage in killing power of the larger diameter bullet going to the 25 already at such a speed. Such a velocity would be within hailing distance of the original load, and the idea is not to kill the gun early, but rather duplicate the 22 or better it. A 50 at 1100 will do this. If RD would still somehow have one of his flatpoint 25 cast bullets available or if you could get Swede Nelson of NOE or some other custom maker to offer the design (he offers RD moulds now.....don't know about the 25 design for the 25 Auto though) you would be in tall cotton.
I would find a powder that gets this velocity and meters well in the small charges and call it good. If I had Bullseye, Universal, maybe Power Pistol or your AA #5 that would be a good enough selection that I would let accuracy and "close enough" velocities make the decision on what to use.
Since tiny charges of large flake powders meter poorly in a lot of measures and I hate to weigh every charge, I'd go after a fast to medium fast speed fairly dense powder of small granulation that meters well. Since double charges won't be a problem there may not be such a thing as "too dense."
Why not try book charges of Bullseye or some other good metering, dense powder and see where they land you. I know this may not get everything the cartridge may give, but you ought to consider what the rifle was designed for and come to some reasonable approximation of that.
I've shot an awful lot of small game with flatpointed 25 caliber bullets at speeds like this. They kill very well, and are a step above the .22.