They used to make a "M" series that was gps/chart plotter only. I don't know if they still make that model though.
What are you doing that requires the faster refresh rate of the gen3? I think it's 10mhz and the gen 2 was 5mhz maybe...
I don't pay that much attention to all that because I've never had an issue with update speed.
I know gen 1 was 1mhz.
But the gen3 is 10mhz and the point 1 is 10mhz, you gain a heading sensor. I'm not sure if the point1 would give you 10mhz on a gen2 or 5mhz. I'll ask on another forum and post the answer.