The accuracy should be the same as long as the GPS antenna is close to the transducer of the unit marking the waypoint ...... and you need to be careful you aren't sharing the bow antenna to the console unit, or that could make it off.
I don't have the HS GPS, but I think you can share the heading indication without sharing the GPS data.
Also, the waypoint is only saved into the memory of the unit marking the waypoint, but will show on both units as long as they are networked.