I don't hunt- but I think any hunter will tell you that at that range it will come down to shot placement...
Keep in mind you're talking identical caliber bullets here- so the difference comes down to the larger case capacity of the 6.5 Creed (or .260) being able to push a bullet of any given weight faster (and natch, the Creed can push heavier bullets that the Grendel lacks the boiler room to handle)
The 6.5 Grendel pushes a 123 grain bullet at about 2600, the Creed/.260 at about 3000.
For specific comparisons, pick a bullet and punch it into a calculator, like JBM, and you can get the kinetic energy at any given range.
Recoil is, of course, going to be a bit heavier on the Creed, but my guess is the felt recoil will be partially offset by the heavier AR-10 platform. Neither will punch hard- one of the reasons the 6.5's are so popular is their impressive ballistics for their weight and amount of powder you need to burn to send them.
My son built a Grendel not long ago- it's a rush to shoot, banging minute of angle plates at 600 yards. But if the additional weight and cost of the AR-10 platform isn't objectionable, for a hunting application, more energy is always better than less...