From what I've read the 420SEL actually gets better gas mileage then the 300. Bigger engine doesn't have to work as hard I guess. The 560 is fast but cost more for gas and to insure. I don't know what you are paying for insurance but I am 18 and got a quote of 3k per year for a 560! To much for me. I am on the hunt for a W126 right now too and am leaning toward the 420, and 300SDL. They seem to offer the best balance in economy and speed. The 420's also seem to be plentiful, at least in my area. Resale is a wash for the gas models, higher for diesel.