Likewise extreme performance, but I would be very interested in longevity. I'm using Metzeler Tourance Next's at the moment, they've worked well so far, I have 7,000 miles on them with lots of tread left. I liked the RS3's on my K1600 and will definitely try the RS4's. Let us know how you get on with the RS4's, I'm sure there will be a deal of interest.
Stay safe and well.
Regards,
Tony