I have 37's on my 2007 JKU Rubicon. I also am running a Rippmods Gen 2 Stage2 Supercharger. With the stock 4.10 and the Six speed I am actually getting a few more MPG's than I was stock. Average MPG 15-17 city 19-22 highway. The Supercharger is an expensive upgrade but I was suprised at the 1-3 more MPG's I am getting, compared to when the jeep was stock on 32's. I am now considering regearing to 4.88's I have plenty of Power in 4L and power through all of my gears in 2H. But would like a little more zing 3-6 gear.
There are gear and tire charts that should give you some insite on where you need to go as far as gearing.
A formula used to help get a rough Idea of what gears you should run is.
New Tire Size, Multipiled by Old Gear ratio, divided by old tire size.
My Jeep: 37 x 4.10 / 32 = 4.74
The formula for my jeep comes out to 4.74 closest manufactored gear sets are 4.88. That is why I am debating 4.88's