I alway figure - the % of oils and fuel should be left alone myself. The companies that make the fuel should no more about what is needed and what is not. So I personally would say don't add any extra oil to the fuel.

Here their are many fuels and %'s to choose from. If you ask fr it, they will custom mix it for you as well. I buy the stuff already mixed from the manufacture.

I run 25% nitro - but there are some with more and some with less oils. The race blends have the least oil. I find with those I get lower temps and it is easier to tune. I tried the one with the most oil, and I can't keep my truck or buggy running with it at all.