IMO, barrel length and not loading quite enough powder is at least part of the issue with getting slow velocities.
In all honesty, if we can only get 2700'/sec then we're probably better off just shooting a 260.
I felt Hodgdons data was a little on the soft end, especially after looking up data on the original 284 Winchester with heavier bullets. They used to run 55-57 grains of H 4831 in the 284 with 160-168 bullets at 2700'/sec. I couldn't think of any reason that 55 grns wouldn't work in the 6.5 version beings we're only shooting 140 grn slugs.
I didn't personally see any pressure signs until I hit 56 grns of powder, and Len said he didn't either in his rifle which is about identical to mine as far as I know. There appears to be an accuracy node at around 2950-3025'/sec in my 26" Brux.
Here's a similar thread just for some more info if anyone is interested:
6.5 x 284 h4821sc 51 gr. 140vdl. velocity?