Keep in mind guys that F Class is not a group size game. It's a scoring ring game.
That being said, when a bullet breaks the line, it goes to the higher value.
All other things being equal, the 30 call by virtue of diameter alone will on this basis produce better scores.
Key point is all things being equal, which they are not.
The energy required to push the heavy 308 round translates to mechanical stress on the system and the shooter. This makes accuracy more difficult to maintain over a weekend of shooting.
I helped spec out a wild cat for a buddy of mine so he could run the 220 to 240 grain bullets using around 80 grains of powder. He admitted to it being hard to take, but for the rest of us on the line it was just as bad and nobody wanted to shoot with him.
Just understand these big guns can be hard to tolerate over a weekend of shooting even if you can shoot it well in small shooting sessions.
Another point is that long range shooting is much like golf. You need a rifle for every shot.
What I mean by this is that big high BC bullets have the greatest advantages in high wind or a fast switchy wind with overcast conditions making mirage hard to read.
In calm or predictable conditions, the smaller rounds usually outperform the big hammers because its an accuracy game.
I've known guys to run a 6BR at 300, 500 and 600, then switch to something bigger for the long range stuff.