Here's my experience.. FWIW
Bought a 338 Win. Weighted just a titch over 9# with scope. By third shot off the bench it was
PAIN!! and that's shouting....... Oh, and was shooting in a tee shirt.
It already had a decelerator pad on it but the surface area of the butt stock is very small and the angle is all wrong.
Put a total of 1.5 lbs in the butt and fore arm. That definitly brought it into more than manageable comfort zone.
I've shot plenty of 300 mags, Win/Wby off the bench usually with a 180 grn bullet moving pretty good. None of them came close to the 338 w/225 @ 2800+.
Long story short - I'd try a pound or so before I went to a brake.
Catfish, I may put a brake on my 270 so I can see bullet impact with heavier bulllets. But that would give me an unwieldy 29 1/2" bbl waving around.