Honestly...how good was the 318...mpg / durability / hp

I don't get the frame of mind of some folks. That somehow the 318 is a dead dog POS just because it was never offered in a real performance version. Kinda like people who piss all over slant sixes. Are those even real Mopar guys? Those two engines are purt near bullet proof and yet get the least respect of any other engines out there. ...and it's always by supposed "Mopar" guys. Chevy and Ford guys appreciate those engines. Just because something won't run nines, doesn't mean it's junk.
When I had slant powered a bodies & f bodies my goal was to smoke the f bodies with the 318's or any gm stuff my buddies had with 250's or 305's. I had the same mildly hopped up slant in multiple cars( I wrecked a lot of stuff as a teenager) and I won more than I lost.

I think by 78/79 a 318 had 140 hp. A stock super six had 110. Not sure what my hop ups were worth but red light to redlight the 318 and 305 with a two barrel didn't have much of an advantage. If they were poorly maintained and I could get the jump off of light I won.