There was a time where four stroke fuel had less oil in it than two stroke fuel, something like 16 to 17%. Different fuel makers had lots of different recipes. Four stroke engines were different then also, and it was common to have to double the displacement to achieve equal power of a two stroke. But as four stroke engines improved, the strict fuel requirements have eased off. I think with today's 4T engines, as long as you use an all synthetic oil in the fuel, you can use just about anything. I run Powermaster/VP Fuels YS 20-20 blend in my Saito .56, and it's 20% total oil (all synthetic) and 20% nitro. It's probably the most popular blend, although quite expensive these days at 40 bucks a gallon, and I imagine some guys may be experimenting with some different fuel this summer. I have run this same fuel in a OS.32 two stroke with no harm done just to see how it would run. In short, 25 years or so ago, you may have had some issues after long term use of low oil four stroke fuel in a Fox.35,  and a sticky valve train in  a four stroke engine from running Fox Superfuel! They would run, but the Fox would be the looser here after several runs! If I have to give up Powermaster for some reason, I will try Morgan fuels 15% nitro Cool Power fuel to see how it goes. I have heard of local R/C flyers keeping only that on hand to run their R/C engines on.
  Type at you later,
   Dan McEntee