Cams are actually very helpful. When I had cruise on and was about 75mph the car didn't have to work hard going uphill. Now, with stock cams, the car has to work and my MPG needle drops a LOT more when I'm going up a hill.
With all my mods, light weight 17s, light weight flywheel, cams, intake, exhaust, 3.46, etc, I was able to get 29mpg cruising on long trips. Around 23 mixed. Mainly stock (big filter, shark, 3.46) I'm getting 22 mixed.