"more ass" = what are your requirements? What do you want to do with this new cartridge which cannot be done with 223 Rem?
No matter what your requirements are, unless you are a masochist, my first suggestion is to buy a cartridge solidly supported by factory brass and factory ammo.
If it is a true wildcat, a non-SAAMI cartridge that requires you to make your own brass with no option to buy factory brass, forget it and move on to some other cartridge.
6mm is a really good caliber. Even the 107 gr bullets offer very low recoil (not much more than an 80 gr 223) and there are lighter bullet options to further reduce recoil.
I have never shot anything except 107 gr SMK's in my 6mm, ever.
I'm not exactly sure what that means but it is a fact. Maybe it implies I've never needed anything else, never felt hindered in any way by the bullet.