it really depends on what you want the fuel for. If you want it in a .12 sized engine, 20% is more than enough. In a .21 or bigger it might be what you're looking for.
I went from 20-30% a few years ago. I hade to lean out my mixture, so that tells you it's working better. Just be careful with your tuning of it. It's no different trying to get a tune but with the higher nitro you will generally see little less oil. That makes being right with the needles alot more important.