If neck/shoulder and recoil issues are a concern, 6.5 is the easy choice of what was listed. 308 would obviously be second. I see no reason for that application to consider the others. I like 243/creedmoor sized 6mms too but that wasn't on the menu.
I haven't seen that. Maybe more "good" brass options but neither is really strained right now. Typically see more factory ammo 243 on the shelf. I shoot 6 creed but really only see hornady precision hunter or eldm match as decent hunting ammo on the shelves with any consistency. Not many standard price point factory hunting rifles chambered in 6 creed. Ruger is the primary one. Tikka, browning, savage, weatherby, etc all have 243 hunting rifles but not 6cm far as i know.