I would contact RIVA Yamaha as they can tell you. I have 2002 XLT 1200 that had oil pump deleted and I run the Yamalube at 50:1 ratio mix, but check with techs at RIVA. 1-877-748-2926 or locally here in south Florida (954) 785-4820
I agree. I have a GP1200 as well and am running premix. 50 to 1 is what my mechanic recomends. Any richer and you are wasting money as well as throwing out oil that is polluting the enviroment. Keep in mind that 50 to 1 is what you need for wide open throtle (WOT). when you are just crusing at say half throtle you oil needs are even less.
As far as the oil that you put in, I am using Yamalube but Amsoil is a great choice as well. Bottom line - don't cheap out on the oil, it is the only thing that keeps you running in the end!