Demon 625

Currently running a 600 eddy on a mild 318. Runs fine but wondering if a Speed Demon 625 might give me a little more pop plus better mpg then my 600 eddy. Just looking for some feedback before making a decision. Currently I get a little over 15 mpg on trips, 3:23 gears. Thanks for any feedback :)
15 on trips isn't bad. I have found with a 3.23 gear and 55-60 mph will get me almost 20 with a 600 Edelbrockon myHp 273 or the stock 2 barrel on my 318.