The 6.5x284 will get it done for sure (my "truck gun" is a Ruger No.1 in 6.5 Norma). The 300 Norma mag is another good choice. I took a doe at 616 yards in SD this year with 220 ELDXs.
I found a good bit of 280ai brass at teton river outfitters in Pierre a few months ago. I picked up a Ruger No.1 in 280AI earlier in the year and plan to load for it. I have a few 284 variants and would jump all over a .284 Winchester if I could find one. Good luck!!!