Well, as you are probably aware, the 6.5 PRC has nearly identical case capacity to the 6.5-284 (depending on your COAL, you might even have more capacity in the 6.5-284. Hodgeon has all sort of data for the 153 Hornady bullet in the 6.5 PRC. The velocities are all slower than I have read from many threads, but at least you have something to go by.
I played with QL for my 6.5-284 with H1000, Retumbo, RL-26, H5831 Norma MRP, Ramshot Magnum and none really resulted in the sweet spot of "100% case fill at max pressure" (I have too many powders).
So I went out and bought a jug of Staball HD..... Another form of addiction, re-enforced by the years of powder shortages.....