My brother has fooled around with a rifle in 6.8 spc. First of all it is a pretty good round, however, it is hard to find and is a bit spendy when you do so. He usually gets Hornady for factory ammo and the rest of the time he reloads. It does have better knock down energy at further distance then the 223. It is a bit more accurate than the 223 but I believe thats becuse of the slightly better wind bucking characteristicts the heavier grain weight bullets offered for the 6.8. The BC may be better but I dont know for sure.
Heres a drop chart or come up sheet for elevation only for this round. It is calculated for a temperature of 70 degrees, 29.26" Hg., 250 feet in altitude, 26% humidity, and using a Hornady factory, 110 gr. BTHP with zero @ 100 yards.
100 yards 0.00 moa
200 yrads 2.25 moa
300 yards 5.50 moa
400 yards 9.50 moa
500 yards 14.0 moa
600 yards 19.50 moa
700 yards 29.50 moa
800 yards 33.25 moa
Hope this helps in your decision.
A good piece of glass is like a fine piece of ass. There is no known substitute known to man, and neither are cheap.