Honestly, I don't think there is noticeable difference at the speeds skaters go, except maybe hill bombing.
I believe Rockin Ron did some engineering speak, with charts and whatnot at one point that proved 6 balls were faster at acceleration than 8 balls and achieved a great top speed.
I've been riding Swiss 6 for years (they just last and last if you maintain them) and just picked up some BigBalls to try out.