6.8 SPC vs 6.5 Grendel - will the arguments ever end??
Whichever you like, 6.8 or 6.5, it's going to be a lighter package than an AR 10 sized .308, however, if you don't need all of that junk on it, a nice wood stocked Springfield M1A is an option. The OP needs to decide what HE wants based on HIS criteria and HIS priorities. We can argue all year about the benefits and shortcomings of everything and not settle a darned thing.