Having done both, in short action, I would go with 260AI. I prefer long actions for the 6.5-284. The next step up is the 6.5-280 imp... not a short action candidate.
With R17, you can get 2950 with a 24" 260 AI and 130 Bergers. With a 27" barrel, I'll bet you can get closer to 3100.
