I believe that with the airbrakes open your safe positive
G-limit reduces to +2.5G. This is because you are forcing
most of the lift to be produced near the tip and thereby
increasing the wing bending moment at the root, and
there is also a hell of a shear force produced. God
knows what happens if you open them suddenly above
Va while pulling 3.5g but i suspect it would not be
pretty. (I also suspect that it may be this that caused
several big gliders to have wings come off in spin
recovery)

I once saw a discus, 'A' I beleive, due a high speed low pass and half
way through his pull up, which seemed to be agressive, deploy his
airbreak/spoiler (?). I thought for sure his wings from the airbreaks
out were going to snap off as they had a significant greater angle of
'bend' than the rest of the wing. I don't know why, but I know what I
saw.

Don