DAS,
On my Dohc Neon I got 28mpg on regular and 33mpg on premium.
Thats a 18% increase on MPG. With Premium fuel only 7% more expensive than Regular, I find it cheaper to run Premium. Dohcs using regular loose 4hp and 6lbs of torque from the factory rating. The factory uses Premium for the Power and MPG tests on Dohc's.
The '95 Dohcs actually have 150hp, after '95 they changed the cam and dropped to 146hp. Since there is less than 5hp diff, they are not required to re-rate the HP. Using regular drops another 4hp leaving you with 142hp.
The Sohcs have a similar story 132hp for '95, 130hp after 95. Take a 130hp sohc and install a performance computer you get 141hp and 140lbs of torque with premium fuel vs a stock Dohc 142HP and 125Lbs torque on Regular, some people with Dohcs wonder why they get their butt kicked by what seems to be a stock Sohc, now you know.