My wife is running a Sig Tango6 2-12x40 on her Grendel. Agree with others 6-25 is a bit much. I like having the ability to dial the power back for close range. At 2x with the illumination turned on you can shoot it almost like a red dot. Depends on your intended application though.
I've got a 4-16 crossfire on one 6.5 Grendel, a 6-24 viper on another, and a 5-25 mark V on a 224 predator. Run what you like, there's no such thing as too much scope. Hell, I've got a 3-9 on a blackout...
That all depends on what you use your Grendel for. Mine has a VOrtex Razor Gen3 1-10x24, but I use it as a general purpose "a little bit of everything", so the Gen 3 is perfect for that.
I've got a Burris XTR II 1.5-8x (CQ mil reticle) on my AR-6.5G SBR upper, and a Tango6 3-18x (DEV-L MOA) on my Ruger American in MDT chassis. No objections to either. The 6.5 Grendel is a round that can go pretty damned far if you give it enough velocity up front, so giving it a little extra scope seems reasonable to me.
Great choice as long as you like it. I have a Steiner T5XI 5-25 on my 6.5 grendel bolt action and is a good fit, cartridge is able to reach distance to warrant the magnification and also my eye sight is not the best.
On my 12” I run a Strike Eagle 1-8. Wife and kids like it for hunting. My 18” wears a Veracity 3-15. I like being able to dial it back especially when the wife and kids are using it. I’m really liking the Grendel so far. Had them using suppressed blackouts because they’re a little recoil sensitive but built the Grendel’s last year. Boy took his first deer and then they all 3 took hogs with them this fall/winter.
I wanted a lighter gas gun instead of carrying around a 308 gasser. So I built my 6.5 grendel and also opted to run a strike eagle 1-8. Shot it out to 600 and very happy with the results. But honestly all my kills have been under 100.
Kinda built mine for a specific purpose, just my experience.