I had just replaced my OEM rear brake pads, at 10,500 miles, just in the nick of time as the pads were very close to the backing plate on the inner pad. My fronts are good for maybe 500 to 1,000 more miles as I must be more gentle with braking and using the front brake. I do notice that when I'm on the road that I will use the rear brake a lot more when going into the corners with some speed, that and all the mud that must get on the rear rotors hastens the pad wear on the rotors, in any case, they pads are now new.
I wanted the same performance as the OEM pads and have always had good luck with EBC R pads which are sintered and that is what I have replaced the OEM pads with. I love that they are only about $30 as Beta pads, and all parts for that bike, are so much more expensive than WR250R parts, yay! The WR250R parts last longer and when they do need to be replaced, they are cheaper, what a great bonus.
I could not fit the OEM backing plate and pad as the EBC pads must be a bit thicker. As someone else on the board had mentioned that they would wait until the pads wear some and then try and fit those dampener pads, I might do that if I notice anything out of the ordinary without using them. My Beta does not have anything extra on the back of the OEM or the EBC replacement pads and I have found no issue(s) so I'll just have to wait and see.