AftergurnerI haven't skied either but from what I have read, the Jmo's seem to be stiffer, so it would probably be a matter of preference. Demo a pair to get a feel. Kartels have sick graphics though, if that's any factor your considering. If your Jmo's are fine just keep them. No need to spend money on practically an the same ski.
B.QuincyYeah basically the same ski just more playful and jibby.
The Kartel 98 is actually almost the same stiffness as the Jmo. The difference is the waist width (obviously), rocker profile, and taper. While they're similar, they do actually ski pretty differently. The 98 has a lower swing weight, they have a little bit more camber underfoot to increase carvability, and the taper prevents catches off jumps. The ski is very much an upgrade from the Jmo, a bit more park oriented than the Jmo was but still really fun outside of the park. I think you should really consider just going with the Kartel.
That being said, the demo fleet will be arriving in PA later this week, keep your eyes open to the ON3P facebook page and event calendar so you can try them out for yourself. The skis really speak for themselves.