Nice trike man!
I run Amsoil Dominator at 40:1 with no trouble even though Amsoil says their stuff is good for 50:1. I'm not real comfortable with 50:1, although I have not had any bad experience or heard first hand bad stories about it. Oil is relatively inexpensive, and good insurance.
As to your question about a chart, I use one of those graduated pre-mix measuring cups. It's graduated for a variety of ratios and very simple and handy to use. I think they only run about $10 or so. I recommend getting one for mixing your fuel.