I've owned both Ontarios, they are indeed good. I'm looking hard at the Condor Moonstalker, wondering if it's a good option to my Becker BK9.
From my experience, if you are wanting a chopper more, get the SP51 with it's saber grind. If you are more oriented towards slicing, get the SP50, as it has a full flat grind. Both can do both jobs, one is just clearly a bit better for the job than the other. Keep in mind, though...both are 1/4" thick. So really, both are going to be better at chopping than slicing, ideally.