How happy are you with the sequencer on your Korg? Have you tried out the sequencer on the MPC?
Personally I wouldn't sequence on either of them, but then I'm a bit slow and need my sequences displayed in front of me in a really obvious way on a computer screen. If you are comfortable with the Korg why change? But if you think you'll be able to do more with the MPC then go for it. Sorry I can't be of more assistance, but these things are really subjective.
KasioRoks