I was interested in the SP100...I'm a die-hard Korg fanatic...but I read a good comparison review in Keyboard magazine, so I did a trial run on both the Korg and the Yamaha.
Yamaha won!!!
I haven't bought either yet, only because I'm really satisfied with Korg products and I'd really like to stick with them...not to mention compatability with my other keys. T1 & T3