Hey BigDog!
You got me thinking, I have always been a 4 into 1 guys myself, yet I am probably as wide as you are!! Obviously you have been checking yourself out in the mirror too? too funny... Seeing how the stock busa sure doesn't need much modification to make in insanely fast. I might just go with a set of slip-ons and keeps the double look. Regular slips ons won't need the PowerCommander in order to run smoothly, once you change the air flow, like race baffles etc, you need to richen the fuel mapping.
A 4 into 1, is when the 4 headers all collect in the same spot and continue as 1 pipe, huge top end results, especially with the duplex crossovers from yosh!!. A 4 into 2 into 1, is when 2 headers join into 1 first, then shortly after the other 2 join into 1 then the 2 midpipes eventually join into 1! Kind of like a menonite, inbreed family! (joke!). With these full systems a jet kit (PCII for EFI bikes) is strongly recommended for max performance. I believe even on a stock bike the PCII can clean up the fuel delivery as the stock system is never perfect. Maybe someone can correct me if I am wrong about all this....