Considering Kumho T121 for 2009 BMW G650GS

This tire has a load index rating of 104 (2000 lbs) while it has a speed rating of M (81 MPH).  The bike in question only weighs about 450 lbs, and this is the only darkside tire that fits the rear rim of this bike.  I'm strongly considering darkside tires after having to replace the conventional tires every 8k-12k, which is too often for me (at least once a year).  My concern, of course, is the speed rating.  I commute on this bike, and I almost never go above 90 mph.  I was hoping that the insane load rating somehow compensates for the speed rating on these tires.  I was recalling that the Iron Butt Rally rule only requires the tire meet or exceed OEM load requirements.

New members are forbidden from posting links, but this is the Kumho 121: T 135 /90 R17 104M T BSW HK, part number 1763413, as quoted from the discounttire website.

Thanks!