Cam vs mpg

[Sawlog]

I have a 69 c10 with a 350
65 cc iron heads with 2.02 and 1.60 valves. 165 cc runners
Performer dual plane intake
600 cfm carb
Headers and 2.5in dual exhaust
Th400 tranny with stock converter
12 bolt rear end with 3.08 gear and 30in tire.
My current cam is 204-214 @.5 and 420-440 lift with 112 lsa.
My question is... what would be the best cam for performance and milage?
In getting 18 mpg now if I keep my foot out of it. Wouldn't mind going a touch bigger if it won't kill me.
Thanks