If you reload I like the 7TCU but my all time favorite single shot pistol cartridge is the 7mmIHMSA which is based on the old 300 Savage, incredibly accurate and has some punch. I don't want to start a flame war but in my Wichita very very few rifles could shoot with it.
ccw1911, I also have a Wichita in 7mm IHMSA. It is the most accurate bolt action pistol I have every owned, and I have owned many pistols. I have a 200 yard target that has a 2" group and nobody believes I shot it with a pistol. It does pack a punch, on both ends. I had to put a muzzle brake on it to tame it down.
I can't help with the 6.8 rem but I have reloaded the 7 TCU for my contender and it is a great round and it does not have much recoil.
The 30-30 contender, 14" barrel with a muzzle brake also is a good one for long distance shooting.