Hey Reds!
OMG...YES, there is a destinct advantage with the upgrade from the 28mm.
D/D is right, no such thing as 30mm 'flatslide', unless it's the knock-off Keihin...and stay away from it...but, go with the flatslide.
Per Ace's advise, I went with the Mikuni 32mm flat on my '99 KS. At the same time I fitted an old BSA shorty exhaust (unrestricted) and put in one of those bolt-in baffles, which sounds awesome by the way.
The increase in performance is remarkable. It feels like a new bike...the throttle response is immediate and she pulls like a bitch. I took the OEM silencer off, which weighs a ton in comparison, and removed the OEM 28 Mikarb. I too, have the KN cone filter.
Perhaps because I upgraded both intake and exhaust at the same time, the next ride out was so impressive and noticable. The climb out from 40-60 is now quite exciting!
I can't say enough about the increase in performance...but, perhaps I have. Sorry....