I have a 2000 RC51. A little insight if you're unfamiliar: 1000CC water cooled V-Twin from Honda. Redlines at 10500RPM. The engine temp usually never sees past 230 degrees, unless I'm stuck in traffic, which rarely happens, but can.

Anyways. I'm wondering if I could switch to 10w-30 to help circulate the oil better. I normally use 10-40, but a buddy of mine bought 10w-30 for his and noticed it a lot thinner and looks like it would circulate a lot better than the 10-40.

If I were you I would stick with the manu's recommendations. Its not that easy to find parts for the Rc51's