Don't have a Grendel, but I do have a 6.5 Creedmore (and a .243 Win) and I do like the way the 6-6.5mm bullets shoot. Don't know how much knowledge would transfer, but to whatever extent you think I could help, just ask.
I own a 6.5 Grendel in an AR15. She is a very demanding mistress. Several friends shot mine and had me build one each for them.. Now neither of their wives will let them come out and play. It is my favorite rifle. We shoot them out past 1000 meters.
Here is my Grendel and a target. I can't remember if it is 400 or 500 meters.
They've finally started producing 6.5 twist barrels for the 224 Valkyrie, which have vastly improved the accuracy. Still remains supersonic beyond 1300 yards. I was all about a Grendel until that baby hit the market...