I always thought my 19mm dellorto was better on my 65 metra than others running a 21.
I am still curious on the polini though. I think the mikuni is a much more advanced carb and if tuned correctly could produced enough power for you guys to blow your polinis up even quicker. Taking it to an rpm range it hasnt seen before, but this is a total guess.
The mikuni flatslide is very smooth and responsive.