Push a 120 to 2600 in a 20" and good luck not blowing brass/primers or an action. Running safe pressures IS of concern to me, perhaps not so much with others.
7TCU in a Carbine rifle will do 120/2550, smaller bore (IE less area on base of bullet for gas to work) plus a longer bearing surface bullet PLUS typically a faster twist - will raise pressure faster and restrict velocity over it's larger bore cousin.
COL is an issue to consider in a bolt. 100s might be best if a 120 cannot be seated w/o eating up alot of capacity. Throating matters but likely mag box will determine COL.
The only way to know what a given load in a given rifle will do is find out, by working up loads safely. I will be interested in hearing your speeds.
What is the Difference in capacity of a Grendel vs a TCU, and what speed will a Grendel do? That's what I would be thinking....one could add 50-60fps with a 24 vs 20" bbl.
2400 vs 2600 is not a game changer to 200 yds, using a good expanding bullet like a ballistic tip thru vitals. YMMV.