Most engines only see a 200-300rpm gain for every 5% nitro you add. Since it’s hard to determine actual engine rpm on buggy engines, you have to judge by how fast your lap times are or how fast the truck can go in a given length of straight track. The reality is you get about 500-600rpm; maybe 1,000rpm more on 30% than you get on 20% and your tuning window is a little wider. But in racing, it’s not the engine you’re running, it’s your driving. I’m willing to bet a better driver using 20% nitro can beat a good driver using 30% nitro.
I’ve used fuels containing 0% nitro up to 50% nitro. I’ve found no real good reason to use more than 20-25% nitro as there is no significant benefit beyond a touch more power.
I’d suggest - for bashing - or even racing - a fuel comprised of 20-25% nitromethane, 11-12% oil, and a medium heat range plug. Ultra hot plugs are fuel wasters. Ive found in a bashing environment in the engines I run, a 60/40 blend of castor to synthetic oil to be ideal and I use hot body medium filament plugs like the Picco P6TH and Novarossi C6TGC/CTO6. Ive used a P6TC Picco plug off road and it ran just fine, but off idle had a little lag as the plug needed to heat back up. Hot body plugs retain more heat and have less lag.