But, why is the E/S the only one that has the different brake pads listed?
don't know why, and the I/S are listed cheaper than the std on directline. I remember a few yrs ago something came up about an addtional backing plate for the I/S rears which the std didn't require. so I surmise the I/S is a thinner pad hence the lower $. The extra plate would be for heat blockage to the pistons in the caliper.
I checked Vesrah, EBC, Ferodo, DP and SBS and all list the same brake pads for all valkyrie models except rune. From some google searches it seams that Vesrah, a japanese co., is the supplier of OEM pads and are the same pads.