Mild Built 340 Timing/tuning help?

I agree about the 110 octane leaded. It could even be costing some power. Certainly costing money!

If you really want some insight as to what octane to run, do a compression test on it and see where those numbers are. That's not an end all be all, but will certainly give you an idea. If you do it, post the numbers up so we can advise further.