I use AMSOIL SAE 20W-50 Synthetic Motorcycle Oil (MCV):
http://www.amsoil.com/storefront/mcv.aspxIt may cost a little bit more but I think it is worth it. Living in south FLA things get pretty hot. Although I don't have any numbers to back it up, I think my RK runs a bit cooler with the AMSOIL syn. In standard ASTM testing AMSOIL performs better than the HD syn3 and HD 360 (and just about everything else):
http://www.amsoil.com/products/streetbi ... Paper.aspx