Having never owned a 6.5-284, I have to go by what the reloading manuals say the ballistics are. I owned a 6.5-06 briefly in 1983 or thereabouts, and I could launch a 139 gr Hornady at just over 3,100 fps IIRC. Looking at the Hornady 7th Edition manual, it says a 145 A-Max out of the 6.5-284 leaves at 3,000 fps max, and the same out of a 6.5-06 leaves at 3,200 max, which pretty much agrees with my experience with the 6.5-06. Since they claim to have used strain guages to measure chamber pressure and keep it within bounds, I will believe that their loads are safely within those specs. Having seen handloaders crowd and exceed pressure limits to get the extra bit of velocity available from a cartridge, I think I am being prudent. Not questioning the velocities claimed, just questioning how they got there.
However, me being a 7mm fan, the whole discussion becomes academic, as I prefer the heavier, higher BC bullets available for the 7mm for long-range shooting.