Like several others here, I have both v3 & v4 installed in different folders.
I've just noticed , though, that some of the common settings are shared _ I was trying to configure v3 to have pathplayer disabled and v4 to have it always enabled, but changing it it one version actually changes it for both versions.

I don't know what other parameters are shared by both versions & which can be set independently - I guess it depends on how/where the settings are saved ?

I've also noticed that I need to wait a few seconds between shutting down v3 & launching v4 otherwise v4 crashes at launch.