Kriers is right that the palm grip makes it easier to stream full mouse, in my opinion, since I know that I couldn't stream half as well with click/x if I didn't lean toward palm grip myself. The extra stability from it is what makes the difference when your fingers are moving quickly like that and can't be expected to control the mouse without help.
I think that play style makes all the difference in streaming speed. I see so many discussions from keyboard players about streaming, but personally I never thought streaming was hard with click/x. In fact, I'd say it's the easiest thing for me to do, and I never met a stream at any speed that I didn't feel I could take on, given maybe a little practice. I have a wayyyyy harder time keeping up with fast singles and complex switching motions on some maps and on most DTs above 120 BPM.
The concept of right handed vs left handed making it harder to stream is interesting, because different hemispheres take dominance over different hands, but my play experience is based in using both hands when I stream, so what I've learned probably isn't sufficient to allow me to comment beyond saying that I could see how you might experience left or right handed play differently depending on your brain dominance, because I seem to remember that one side tends to take in visual and tactile information and ultimately relay it back to the other side. I'm not sure if this changes with hand dominance, but it might be the case that there's a certain delay in information transfer for people who have one side dominant vs the other. That's just what I seem to remember reading about somewhere, I wouldn't call it real evidence.