Wow 8 gallons of gas, that's a ton of cutting. It's nice that you volunteered your time to help out. Was there other guys cutting with you or would you rather just be on your own so you don't have to worry about somebody else getting you hurt?
Run whatever ratio you think you need, overkill with the oil definitely won't hurt the engine, it just isn't necessary. Manufactures have to idiot proof there equipment so a little more oil is a safety net for their warranty department.
you can run as much oil as you want but any 2-cycle will run on 50:1 and I will bet the farm on that. If a quality oil is used there will be no issue. If you can find compelling evidence to dispute me then we can have a constructive conversation.
It has everything to do with viscosity and mixture density. Carb jets and mixture can only be metered through jets and passages properly at a certain viscosity. Jetting is calibrated for a specific flow under specific variables. 40:1 is a negligible difference but the principle still stands...