I think the SP-2 is more of a riders bike. It's definately not as good for commuting on, especially around town as it has a tall first gear which means you need to slip the clutch a fair bit. Down gearing would help this but its only got 4900 miles on it so the original is no where near worn out yet.
The Busas engine was amazing, I have to say that. I had an Akro system on that with a PC and it was putting out 172hp @the wheel so went like stink. The Busa is very smooth compared to the SP-2 too. Though you will know this as you have come from a big V-twin.
As you say though the sound of a big v-twin with a system is awsome.
The SP-2 is a totally different ride. I found the Busa a nice bike but really it wasn't a bike that made me get up and feel like I wanted to ride it. I don't know why though. I just never clicked with it like the GSXR's I had had before it. The SP-2 is far from the GSXR 600K1 I had too suspension wise, though I'll get that sorted soon enough
Edit: by riders bike i mean its a bit more involved than the Busa.Like some cars are more drivers cars than others.