From what I understand, a lot of folks whose bikes came with the 6 pots, most of them swap them out to the 4 pots for better feel (at least on the track anyway). No difference in power and the pads are cheaper as well. The B12 guys are the ones to ask as they commonly go to the 6 pots. Whether or not its the case is another story.
The two pot caliper on the B4 is quite good. Looking at the pads side by side with the 4 pot, there's more pad material on the disc. With good pads and a braided line it stops well. Very well. For just tooling around and backroad riding, I'd keep it and run it.
What you get when you go to the 4 pot is better feel especially when you're trail braking hard into a corner. The two pot at that extreme end feels a little wooden in comparison just because of it's design. Best part is that it uses the same master cylinder. I'm sure the master will move enough fluid for the 6 but I've never tried.
I've been quite happy with the 4 on my bike and the few track days I've done with it. I'm sure a hot rodded 2 pot would have worked just as well but I took a chance to get a better brake (since us in the US only got one) and am pretty happy with the results.