Dan, I've been around 6mm's for many years. Built a 6mm Rem. on a 98 Mauser action for my 8 YO son in 1968 and he shot a lot of deer with it before he was big enough to handle the 30-06.
My current favorite coyote/deer/hog rifle is an AR in 243 WSSM (Because I'd rather hunt coyotes. There is no significant difference in velocity than 243 Win and about = to 6mm Rem.). I've shot a ton of hogs with it and shot placement is king, especially on hogs.
Couple of things I have learned over the years about the .243's:
1) They cannot be relied upon to leave a strong blood trail. I loaded 100 gr. NP's for son's use and, while they can usually be relied upon to exit, the blood trail is still pretty weak sometimes.
2) Most deer and probably all hogs will travel 40, and sometimes 100 yards w/double lung shot unless you "break them down". That is, break one or both shoulders or as has been suggested a central nervous system hit. IME, many, if not most, will do the same even if hit with larger calibers as well.
3) I really can't see much difference in performance between the 6mm 100 gr. NP's and the 100 gr. SB. having never recovered either from an animal, but haven't spent much time looking for them, either.
3) Most standard cup and core bullets will out perform the partitions in the accuracy department, but not so much as to nix the partitions for hunting.
IMO, the 6mm's biggest disadvantage is the minimal blood trail and I don't believe you're going to find a bullet that will improve that. All any bullet can do is provide an entry and exit and smaller holes just = less leakage
.
Good luck in your search for the perfect 6mm bullet, but I believe you're getting pretty close right now.
Regards,
hm