I’ve experimented and found that if I fit the Grip, I can hand hold for 2 stops longer in the portrait mode.
I’m comfortable shooting below 1/100s, even 1/40s with some losses, whereas without the grip I try and stay shorter than 1/249s. Must be down to camera movement and of course this may only apply to me, but I’ve tested this enough to be certain. To test I stood in front of a mirror and focussed on the lens text with lenses up to 180mm.