One of the primary reasons to choose 6.5 over 260 is to get a 1:8 barrel. Never heard of one with a 1:12.
The primary reason why the 6.5 comes with a 1:8 barrel is to be able to shoot 140gr + bullets. That is what the cartridge and the rifles are designed around.
I wouldn't think of anything less than 130 gr. The new Hornady 140, 143 and 147 ELD bullets are proving to be absolute tack drivers. They are available as factory loads at reasonable prices. The 143's are a hunting bullet, the other 2 are target bullets. Might want to try a box before investing in a bunch for hand loading.
Walmart is selling Federal match ammo with 130 gr Berger bullets for around $28/box. I tried one box. They were OK, but not as good as the Hornady loads.
I've settled on the 143 gr ELD-X for mine.