The 6.8 SPC has been around for a few years and has its fans.
A wildcatter came up with the .277 Wolverine, which is a resized .223/5.56 case containing the same bullets at the 6.8 SPC (basically lighter .270 bullets than are typically used in the .270 Win.
That conversion only requires a barrel change, where as the 6.8 SPC requires a new both and new magazines. (Making it a lot less attractive to civilian shooters with a lot of AR-15 parts lying around.)
No, sorry I'm not an ammo/ballistics guru.
If it's the 6.8 SPC II, then it's essentially a .270 Short
I've got one, it's GTG for the usual fodder and realistic hunting distances for deer and pigs.
There's always detractors and ignoramuses. d;^)