Yeah I know all that...well versed in it actually. I guess I should say that a 1-7 isn't going to do any harm and there will most likely be zero issues. I've shot 6.5CM and 260 Rem in 1-7 in the past and they performed fine. Anything tighter can get squirrelly., but yes, 1-8 is the generally accepted spec for a 6.5.
Well, I doubt you'll overstabilize in a 1:7, but I'm betting you'll have to shell out for a blank and then have CLE or Craddock etc... custom spin a barrel up for you.
I've looked at about a dozen sites now since we started this, and I've yet to find any production or semi-custom place yet that offers anything but 1:8 for the Grendel.
The good news is that there are a lot more products on the shelves than there were 1.5 years ago.
I run a 20" Wilson Combat on my pig rig and quasi-target Grendel. It has shot quite well with the 100gr TTSX, 120 NBT, 120 TSX, 123 SST, and 123 CC. Next up is the 120 Gold Dot once my shoulder heals up well enough to get back out there.