I have a 12 vane setback 144mm in my Matrix and an 8 vane 140mm non setback in my wife's SJ and they were both huge improvements in surf. I've never swapped them for back to back comparisons but both skis react the same in whitewater as I would expect and the 8 vane had just as much improvement as the 12.
I was on the fence when I first got mine and my transition is actually well documented in a couple other threads. Some say the Mags have too much hookup for surf riding and I thought the same but quickly discovered that the pump was not the culprit. When I swapped in a stock pump, my ski would still not slide out like Scott's AND I lost all the hookup and thrust that I was so used to. The mag is the chit for a reason.
Even my wife noticed that the Mag was a huge improvement. Granted the 8 vane is not as aggressive but it was still better. I installed it in her 07 SJ with the ported 760 and just told her I swapped the impeller. Her very first session and she came back and said the slip/hesitation right off the bottom was finally gone and that she got tumbled in some whitewater and the ski hooked up and pulled her right out of it like it had never done before. She freaked when I told her what I paid for it but she wouldn't let me take it back out so what does that tell you?
Edit: If I rode as much surf as Idok, Wideopen and many others, I would probably agree with them but I don't/can't and I will never get to that point where my riding is fluid enough. I knowingly use the Mag pump as a crutch and I am okay with it. :bigok: