Go with the BMW heavy duty springs
Hagon or Progressive shocks on the back side are a good choice if your not concerned with the purist look of OEM stuff. I think you can talk to either supplier and get a good rear shock that works for your weight, load and riding style. I put progressive springs in the front of my R 60US and haven't been happy with it since. I put 5w oil in and it is still to stiff. The front end is nearly identical to your /5 front end. Heavy duty springs and 7.5w oil in front and a Hagon "built for you" on the back should make things good again.