I've also read where the army is testing a 6.8x43 cartridge.
That would be correct, sir. Remington has finished development of the 6.8mm Remington SPC (Special Purpose Cartridge) and it is being evaluated by the military. Specs as of now are 115 grn FMJ at 2800 fps. It is supposedly lethal out to 500 meters, which seems quite reasonable. It is based on the 30 Rem case and is designed to function in M16/M4 type rifle actions. Remington is also rumored to be developing Tactical Model 700's for urban police sniper use in this round.
If this cartridge is accepted, it will be quite an odd-ball. Old-school military cartridges such as the 7x57, 6.5x55, 30-06, 308, etc. were able to be successfully used as very excellent big-game cartridges. The 5.56 proved to be a most excellent varmint cartridge in its civilian version, the 223 Rem. I don't see the 6.8mm SPC as being very useful as either a varmint cartridge or a big game cartridge. Some report that it would be in a similar class as the 7-30 Waters, but even then I am skeptical. On the other hand, the 6.8mm has been reported to be an excellent target/match cartridge. Perhaps it will see its greatest usefullness going neck to neck with 6mm PPC's. Only time will tell, I guess.