In my OS engines I always run what the manufacturer recommends... why mess with a good thing. I run either 10 or 15% nitro and 18% oil with the oil breakdown to be 80% synthetic and 20% Racing Castor. Wildcat fuels does the trick for me... Now if you really fly a lot and go through some fuel you may want to look into mixing your own, it is cheaper.

Go to the fuel forum here... there is lots of good info on fuels, mixing your own, what more or less nitro does for you... etc....
http://www.rcuniverse.com/forum/forumid_161/tt.htm