Re: 6.5mm hunting cartridge?
6.5 SS, 6.5x47, 6.5creed, 260 Rem/260 AI.
All short actions. 6.5SS would be better than 6.5-284 due to the short action and from what I see it outperforms the 284 by a couple hunderd FPS.
If it were me and building a custom Short Action it would be a SAUM or the SS.