Sorry I wouldn't like to give specific recommendations without knowing more, and I'm not a trader here any more either would will be more generic. But in general terms meth mixes will require a remap whereas mixing some race fuel is probably going to be safer. The Sunoco GT Plus is very good fuel, and one of the other benefits people don't realise is the cleaner burn and so on. I can't tell you what it's like mixed at say 25% but normally when you're diluting with such fuels you end up with the average octane level (not like an additive like lead, MTBE or Manganese which changes how the fuel behaves).

20% methanol as an octane boost is pretty good, but the scope to get the mix wrong and not matching the map is huge unless you've got a small race tank or something.

I do have some data on mixing VP Q-16 from John Felstead. We tested his car with I think a 10 or 20% mix and the AFR was unchanged, but det resistance increased. Q-16 is leaded and a dense fuel so although oxygenated it doesn't have a huge impact on AFR in low doses. And you shouldn't kill your sensors with that little lead if used a few times though the year.

The Lucas octane booster seems to work very well too, along with Webster's "Power Pour"