I will say there is something to be said for an aftermarket power/mileage cam grind. I had one in a 250 straight six in a gmc pickup. It knocked down 17 mpg in a 4000 lb pickup empty or even loaded with a ton of scrap iron (I hauled 100 tons over 6 months) consistently and it had plenty of balls doing it.
I would call your preferred cam grinder, tell him your combo and your goals as to mileage and performance.