We are in the process of the switch from 7.9.1 to VX.
Our new design projects are being done in VX1.1 and we find it quiet stable environment.
Older legacy designs we still maintain in 7.9.1, but expect this will change in the future and we will ditch 7.9.1 usage completely.
With regard to the libraries we currently have two being maintained 7.9.1 and VX. To create the VX library all that we did was a copy of the 7.9.1 library and rename the folder. When we create new parts/cell/symbols we currently create them in the 7.9.1 library and then "export" them to the VX library. Items created direct in the VX library have extra parameters and therefore cannot be "exported" into the 7.9.1 library.
Both 7.9.1 and VX can be installed and a pc together and then use the MGC PCB Release Switcher utility.