Bruce,
The 25% is fine for general sport flying on the reedies. If you eventually get to tweaking the reedies to make a Venom or Killer Bee clone, then a step up to 35% is good. I know a lot of guys use the same fuel as they do for their larger engines, but I've never been satisfied with the runs you get on 5% and 10% nitro. The lowest nitro content that Cox sold was 10% in their blue can Glow Power fuel. But I didn't care much for that in planes. More for the Cox cars and boats. I preferred the Cox Flight Power fuel as a minimum, which had 15% nitro, but usually bought the Cox Race Power fuel if I could get it which had 30% nitro. All Cox fuels had 20% oil, 18% being castor and 2% being synthetic Dow Lube (Klotz). The Brodak fuel is 22% oil, half castor and half synthetic. That's more than fine for the reedies. I once read that you can go as low as 5% castor in something that Paul Gibeault wrote somewhere. But I'll stick to a minimum of 10% castor with the rest synthetic.
But, luckily for me, I have a local speed shop that I can buy nitro and methanol from, so I can just mix up what I want. One day I'm gonna mix up a pint of 60% race fuel for the fun of it. No one does racing around here, but I have a Cox magnesium race pan and the fiberglass top for it, and a left-hand crank for a TD, so I might as well give it a go once in my life.
Mark