Retumbo is a solid performer in the 6.5x284. I would work up from 55 grs. With 140 gr Bergers/JLK's , my rifles produce 2950-3000 FPS with 57.5 gr. using magnum primers. I have never tried AB's but my VLD seating depth is .075" off the lands. H4831sc is anther good powder, but velocities will run 50-75FPS slower, charge wts. of 50-53gr. I have no experience using H1000 in this caliber.
"Let us speak courteously, deal fairly, and keep ourselves armed and ready"-T. Roosevelt