I had the opportunity to play around with the casio a few weeks ago, and while their style files are great, their individual instrument sounds are awful--especially the paino. Neither keyboard is suitable for gigging, however, the Yamaha is likely the better choice for all around sound quality. If you're serious about performing, you'll have to spend a lot more money, but in the long run, the higher priced machines such as Yamaha's 2100 and Tyros are both good investments. The same holds true for high end models of other manufacturers.

Good Luck,

Gary