I have been with Mixvibes since before CrossDJ, and the same thing happens to me, I have the U-Mix Pro2 controller and with CrossDJ 4 it is very slow and not very stable. And yes, for me version 3.4.3 is much better than version 4.
Now I am considering changing software, the problem is that changing software means changing controller as well.
Traktor will have to be tested