ML has some smoother animations like scrolling. Otherwise I also would agree in the general Speed and ability to handle huge multi tasking workload ML is worse than SL. I am not sure what it is but something with the RAM is still wrong in ML. When I reach a certain threshold of open windows and apps, SL did fine but ML gets sluggish and significantly slower. Might also be that due to more GPU integration context switching is slower.
I think in pure application performance. The speed of the app currently in focus there is no difference at all, or none one would feel. But the OS in general imo got slower and some smooth seeming animations don't really hide that fact.