In past 6.5x284's I have used the older 142 JLK and the 142 Precision. The SMK as well, but what they are they didn't do it for me. Most 6.5x284s will struggle to top 2800fps with a 140. My 26" factory barrels (Cooper and a Savage) would just make 2825 on a hot day with a case killer of H1000 and the 140 berger. I am a hunter first and foremost and have seen enough marginal bullet performance at LR. I have sorta settled on 2900fps/.450 BC as minimums for what we do here. More of the BC preferred and a min of the FPS at muzzle.
Currently I am using the 140 Berger (well no, currently my rifles are apart, I ain't using nothing') in a to be finished 28" heavy rifle, but in a pending lighter weight 6.5x284 I will be trying the 123 Hornady as its barrel is 23".........
I guess to say, 140gr is enough. The former Savage got a lot of work but ran out of ele at 1220yds. The former Cooper with a 20moa U.S. Optics rail and a 4.5x14 zeiss went to the mile gong about 90 of the 100 or so rounds I fired from it.