If the only two choices are the ZX10 and the R1, my choice by far would be the R1. It handles much better than the 10 in stock form. It will build your confidence much faster than the 10. The 10 has a tweak more meaness than the R1 but you'll never know the difference when you twist the throttle. I have ridden both and the R1 is just a better bike all the way around in stock form.
However, the GSXR kicks both in the arse when it comes to competition. I have two GSXR1000's and dearly love strapping one to my underbritches. And, you can buy the gixxer for less money than either of the two preferred bikes.
However, I'm curious why you would rather have a second bike that costs more than your busa to beat around on? Why not just ride your busa and enjoy it? I didn't think it rained that much in Florida?