Re: 6.5-06 Ackley or the 264 Win Mag
I have owned the 6.5-06, 264, and the 6.5-06 AI (current rifle). With a 26 inch barrel I think the speed of the 264 and AI will be within 50 fps, but all three will be very close.
Ease of brass prep: 06>264>AI
Ease of accurate loading: AI>=06>264
Light Recoil: 06>AI>264
Consistent velocity: AI=06>264
Reloading dies: 264>06>AI
This is not perfect data, I understand the short comings of my anecdotal evidence, but I think you will find similar results. The 06 case is near perfect for this bore size and inherently very accurate, the same can't be said for the 264. I choose the AI because of the case design and long range performance. YRMV, but there aren't many 264 target guns out there. Talk to owners of all three and see how that 264 compares to the 06s.