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6.5 Grendel drops and performs similarly to 308 Winchester. 308 also drops similarly to 556 as well. So I do think that the 556 reticle will match up to 6.5 Grendel once you do zero the optic. Side note: I have an AK 6.5 Grendel with a PSO scope that is BDC calibrated for 7.62x54R, and it matches the drop to 600 yards. And 7.62x54R matches 308 drop too. Short anwser is YES.
I would recommend an optic with a higher power like 12X or 14X if you're gonna be running a barrel that long. An LPVO does not have enough magnification to meet the capability of the 6.5 grendal considering it can reach out to 800yds.
The acss nova should work fine for 6.5 grendel as it is marked in mils, and if you are familiar with using mils. The others have ballistic drop reticles that are caliber specific for 5.56 and 7.62 and may not be useful. Visit primary arms website for more in depth information on their optics and options.