I have shot the throats out of 7 different barrels chambered in 6.5 X 284 shooting long range competition, so I know a little about the 6.5 X 284. I have had the best combination of accuracy and velocity using either H4350, H4831 or VV N160 behind 139/140/142 class of bullets. I use Lapua brass and CCI BR-2 primers. I really feel that VV N160 is a little easier on throats from my experience.
For the 120/123/130 gr. class of bullets I would look to H4350 first. It works very well for a competitor I know and shoot with. He uses it behind the 130 Berger. Additionally that powder works very well in my 260 A.I. behind the 123 Sierra MK. I am getting 3160 fps out of a 28" Krieger barrel.
As expensive as the VV line of powders have become in the last few years, I would probably lean toward H4350 or H4831.
Hope this helps some.
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