I think your experience with the 22-284 is closer to the reality others have had and completely pours ice water on the old claims of 6,000+ fps. Your loads are slower than my 22-250AI's, which are using less powder than the 22-284. I can push 75 Amaxes @ 3650 with 7828SSC, but due to having several 8 # jugs of IMR4831, I load 41gr under a 75 Amax @ 3,410 fps in a 26 inch tube. That load is case sparing and shoots in the .2's, and while the 4831 will drive them to 3,550 before pressure signs, the groups begin to increase slightly. 50 gr bullets can reach 4,000+ fps with ease, and with the right powder, 55's will get there also. 40 gr bullets have reached 4,500-4,600 fps, but again, I prefer to keep them in the 4,300-4,400 range.
My barrels are either hand lapped by me, or I use Tubbs Final Finish kits before load development. Copper fouling is greatly reduced and I encounter no erratic pressure spikes nor fliers.
For a while, the 22-6mmAI was to be the hot rod round and proclaimed to be far superior to the 22-243 versions and Cheetah I & II. But like the 22-284, it was reality and the production of readily affordable chronographs that ended those claims. Same has been said about many such claims above the 5,000 fps line.