NGK (7415) DCPR8EKP Multi-Ground Spark Plug, Pack of 1
is the one recommended directly from NGK's U. S. tech line for the R1200RT. I've used two sets, at approximately 24k each, and have had no problems. I also don't think they needed replacing at 24k miles. I'm going to run the current set until one of three things occurs: I get tired of the bike and trade; I notice a drop in performance; or, dang, I forgot the third thing.
Not hard to find, Amazon has them and will ship free; if you go to an auto parts store, use the "7415" part number rather than the longer one, if they can't find it under the longer one.
2012 K1600GT: TICKETMASTER