I have shot the 6.5 Creedmore for some time now. I have a buddy that loves to build AR's and wanted to put together another one for me. I have a bunch of 5.56's around, so I told him to try one in 6.5 Grendel which he had never done and welcomed the challenge. To make a long story short, it shoots like a champ and I have shot a bunch of hogs with it so far. I would probably have taken it out deer hunting with me as well, but I have it set up with a night vision and didn't want to go through all the work of removing it, reinstalling and sighting it in again. I put a suppressor on my Grendel and it really cuts the blast down a lot too. My buddy just finished up another one for me that I will set up with a standard scope for daytime shooting. My Creedmore has been sitting in the safe for some time now and relegated to "back up status". I personally really like the Grendel caliber and have stocked up on brass and bullets as I think it will be with me for a long time.
Here is an post that has some info on short barrels for 6.5 grendel. I'll have to admit, it has me convinced you can get near to full combustion with 12.5" in a Grendel. It makes sense to me given the magnum primer and the short/thick case compared to even the 5.56. Seems to me based on the muzzle velocity results from this posting and good bullet selection, you can reasonably hunt within a couple hundred yards.