To the OP, chances are that bullets ranging from 85-140 gr. will work well enough for you if you have a standard 1:8 twist rate.
If for hunting, like others, I tend to be a fan of lighter Grendel bullets (but only certain ones) for hunting. I also like some heavier 130s as well. It just depends on what you want from the rifle/bullet/target combo. I don't know that lighter bullets work better per se. They all seem to do well within their own parameters and whether or not they work well for you will depend on our wants/needs.
140s are NOT too much for the Grendel, but they are pretty much at the top end of heavy bullets. It starts getting tough getting the proper amount of powder in the case when you get above 140 and you may find it difficult to properly load 140s with some powders or cases withe slightly reduced capacities. Previously, I have tested some 140 gr. Nosler BTHP on hogs and a 'buck' (see below).
https://youtu.be/38Qb-BjA3j0
https://youtu.be/BvtAMZuW5jg
https://youtu.be/0_UR3y4CZ2Y
I also have some 140 ELD-M and Interlocks to try out that were loaded by Druid Hill Armory.
Now, if you are just plinking and/or doing some hunting, probably my favorites are 90 gr Speer TNT bullets. They are best on larger varmints (beaver/coyotes) or medium/large game (deer and hogs), but they basically explode inside the animal. At 90 gr., they are fast for Grendel bullets and with the rifle rifle should get you 1 MOA...plus they are inexpensive for hunting bullets.
The most destructive bullet I have shot from the Grendel is the 130 gr. Berger VLD-Hunting loaded by Precision Firearms. These do NOT perform as advertised and do not deposit all of the energy inside the animal. Instead, at Grendel velocities, they tend to break up, but then make for large and long wound channels. While I still have about 150 of these onhand, I don't hunt with them because I don't care for the lower velocity when it comes to leading running hogs and the more holdover needed at distance. I prefer faster, flatter trajectory bullets for less lead and less holdover inside 300 yards, but the damage done by the VLD-Hunting is just impressive (fired from 20" barrel, IIRC).
https://youtu.be/wqKHml1J-bw
I have a 28" Grendel build that I am looking to see what sort of extra velocity I might be able to get out of these same loads and also see what the performance looks like on hogs. I hope to also compare that with a 12.5" barrel in the near future as well.