As far as I know, the best options for lightest weight cameras with APS sensors are the Sony Nex series and Fujifilm X series. The Samyang 7.5mm and 8mm fisheyes appear to be excellent and popular choices for using with these cameras. In my experience, 5 shots around works best for these cameras.
The RS-2 has a 5 stop ring available however overall it's seems a bit overkill for the size and weight of these camera lens combinations.
The RS-1 is lighter and personally, I prefer the friction upper rotator for light setups. However; the nearest rotator option that would work is 6 stops. I could go this route but I hate to shoot 20% more shots around than is really needed for excellent results. When doing a virtual tour and using HDR this can really add up. I could use a 10stop rotator but when working in a hurry that presents the risk of not skipping a stop at some point then realizing later that the set has been blown.
Is it possible to get a combination of the RS-2 lower assembly with an RS-1 upper rail?
Are there others here who use the Samyang/Rokinon and would like to see a 5-stop option for the min-rotator?