Re: Which 6.5 ?
The Savage Predator does not come chambered in any of the cartridges you mentioned. The 111 Trophy Hunter XP, however, is available in all three chamberings. If you want to shoot factory ammo, go Creedmoor. If you are going to handload, the .260 or 6.5-284 are the way to go. Lapua makes brass for both cartridges. It's worth the money, IMO. Of the two, I would go with the .260. I say that because my favorite 6.5 is the 6.5x55 and the .260 is pretty much the short action equivalent.
I have rifles in 6.5x55, 6.5-284, and .264WM. I really like the 6.5x55. It is probably my favorite of the three. It's mild mannered, teriffically accurate, easy to load for, and all the top quality components are available for it. Mine is built on a Zastava 98 pattern commercial mauser. The old Swede belongs in this rifle and shows it by the way it performs.
My 6.5-284 shoots well, but I am kind of underwhelmed by it. I am still trying different loads with it, but so far, I have to really push pressures to get it to perform to a level where it offers any advantage over the 6.5x55. I have been loading with H4831 and intend to step up to Retumbo in hopes that the cartridge will come alive.
My .264WM spanks my 6.5-284 in every way. You are going to pay a price in barrel life with either cartridge. If you want to go for something above the performance level of the Creedmoor/.260/6.5x55, I say go high or go home. I much prefer .264WM over 6.5-284!