If I wanted 6mm performance and it to fit mag length a 243AI with an 8 twist would be the one.

I'm getting 105hpbt and RL 26 at 49grains at 3170 fps. In a 22" barrel.

50 or 51 is max just not what my gun likes. One could get 3200. A 85grain TSX at 3400+ would not suck.