Thank you for the answers, all.
I've since narrowed it down to 6.5 Grendel vs 7.62x39, and willing to call that a wash....unless you're reaching out there. One has a lot of cheap surplus, the other has range and a wider selection of monos, which I like. Although reloading the 7.62x39 with 110 and 120gr Barnes Tac-Tx and Hornady CX bullets for the 300 BLK is working, the fact they cant fit in mags due to OAL issues is a bummer.
Course, there IS 300 BLK as well.
Anway, appreciate all the input! And Dana, your comments are still relevant!