Let's do some math. Let's figure a 1,000 trip. If you get 9.5 MPG you will use 105.26 gallons of gas. If you get 8.5 MPG you will use 117.65 gallons of gas. That is a difference of 12.39 gallons over 1000 miles. At $3.25 a gallon (arbitrary number) that will cost you an extra $40.26 for the lower mileage rig over a 1,000 mile journey. In my opinion these are insignificant differences. If someone wants to check my math, it would be advised as I wasn't the best student and it was a long time ago.
Buy what fits your needs and don't worry about the MPGs.