First of all, from experience, going from a tire that measures 31" on the Jeep to a tire that measures almost 34" on the Jeep is a big change. Your acceleration, braking, and power will take a nose dive. This means your fuel economy will also take a nose dive. I expect that if you drive it exactly the same, you'll lose 2-3 miles per gallon.
Second, choosing the Falken tires hurts even worse because they are some of the heaviest tires on the market. And all that weight is just brutal on fuel economy and drivetrain parts. The Falkens vs. other brands is worth about 0.5 to 1.0 miles per gallon.
So in the end, you're going to lose a signficant amount of MPGs. Currently, every 1 MPG is worth almost $20/month to the average driver in the U.S. So, losing 3.5 MPGs could be like adding a $75/month payment to your checkbook.
But, it will look cool.
~Lots of modded Jeeps and a Toyota 4Runner~
My favorite quote from the press release.. sad but true: "Chrysler claims its products, especially the Jeeps, can handle all sorts of terrible conditions, churning through muddy swamps, climbing mountains, and crossing rivers. Turns out they cannot even handle a car wash."