My 340 build

That is considered safe from all I have every read/heard. I've run a few thousandths more, but I tend to not want to not worry over it even with long term wear etc. Your next step up is either a Cometic gasket at .045" (but you milled surfaces may not be quite right for an MLS gasket) or the standard kit Felpro 8553PT at about .050". The thicker you make it, the less effective the squish/quench action gets. Going to the thicker Felpro will lower static CR by about 0.2 points.