MPG - no difference here.
I mostly drive back roads to/from work which cover small hills in MD and most never get over 40 mph. I get a VERY solid 13.9 mpg always. Which is exactly what I got with my dueler stock tires.
I have had the VX out on a couple of longer trips (~120 mi) and got a little over 16 mpg for the tank which still included mostly back roads. My guess is I was probably getting close to 18 mpg on the highway.
Jay