Sounds like a viable plan Stan. I run Mobil1 in my Cayman(factory fill spec.), I think it's 0W40. I also run 5W20 high mileage Mobil1 in the Dodge truck. Like you say, it's available everywhere and doesn't break the bank.
I may switch to this 15W50 in the Spyder if it works for you. I've been running Valvoline 4 stroke motorcycle 10W40, it's got the ZDDP that we and the Harley guys need.