FWIW, I've noticed running an FAI mix in an engine that will tolerate it (i.e. not very low compression engines) tends to run a bit longer than the higher nitro mixes because you usually lean the needle a few clicks on the FAI mix. Most larger engines will tolerate FAI fuel OK. I've got a little ST G.34 that is a screamer with a no-nitro 75(meth)/25(oil) FAI mix.