Running on a Ninja 13ci tank regulated at about 950psi, I'm getting 900fps with 8.4gr JSBs, all self-modded. It shoots sub moa at 50 yards which makes up for lower power of .177. It gets about 100 shots from 3000 down to 1000psi (still room for improvement here).
The regulator comes at about 850psi from the factory which will hinder the efficiency and power of a stock QB79. The lack of volume in the gun makes for a challenging tune. I had some trouble reaching 12fpe at 850psi and it was very inefficient (even with a lightened hammer and shortened spring) which is why I decided to up the regulator pressure a bit by removing the coil spring and replacing it with the appropriate belville washers. Both power and efficiency went up greatly with the new output pressure since it it closer to the "sweet spot".
Learn from my experience, and that of others...If you want a good bit of power from the QB79 do yourself a favor and make the first step changing the regulator to 1000-1100psi and go from there. 22cal is naturally going to be more efficient and produce more power from the get go, but I think a 1000psi output will make your life much easier in achieving a well rounded tune.