Eric, your Garmin Nav IV should work just fine if you want to use it. The Nav VI is the most recent BMW badged model — it has been known to have problems with the screen but Garmin is good about replacing it. I’m not familiar with the regular Garmin models but I think there is a relatively recent one. Others may chime in on this.
I have a mount on each of my bikes so I can use my GPS unit on all of them.