I have flirted with that caliber but I do not relish the idea of maintaining another library of cartridges to feed it. You are correct. The BLK really shines in a SBR, canned variant with subsonic rounds. But, damn... those rounds get pricey especially if one goes with Hornady..
I have also been intrigued with the creedmore but... again, I hate the idea of buying another 1,000 rounds to keep in stock.
Wolf offers a really cheap 6.5 Grendel that performs -OK- for 8 or 9 bucks a box. It's steel cased blasting ammo , but it feeds and functions pretty well.
The American Eagle 123 OTM is VERY accurrate, and has really good brass for reloading.
Handloading is where you'll REALLY get the bennies out of the Grendel.