I have a 2010 JKU Sport auto that was on 33s and had been thinking about upgrading the stock axles with 4.88 gears and lockers. I had also considered getting Rubi axles with the 4.10 gears from a forum member. I then decided to wait a couple of years until I could upgrade to a Rubicon with the 3.6 engine and 5 speed auto. I have a superchip tuner and run the 87octane tune. Earlier this year I went to the dealership and drove a couple of the 2014 JKUs, a Rubicon with 4.10 gears and a non rubi with the same 3.7 gears that I was running. I really couldn't see a big difference in power from my 3.8. I suppose the 3.6 really does have more power, but seat of the pants it didn't feel like much at our nearly 5k altitude.
Recently another forum member listed his Rubi axles for sale with 5.13 gears and other upgrades. So I decided to stick with the 3.8, only 33k miles, and do the Rubi axle swap. I am really glad I did! I've completed the swap and increased the tire size to 35s and the gearing is perfect. Even with the larger tires the overdrive is more usable than it was with stock gears and tires. And I now have lockers front and rear. Waiting until I could buy a Rubicon would have involved starting all over again on my mods as well. There has been a fair amount of forum traffic about problems of one kind or another with the 3.6 and that was also a factor in my decision.
So I've spent quite a bit of time considering the pros and cons of the 3.8 and am really content with my decision to stick with it. It is too soon to tell how bad my mileage will be hurt by the lower gears and bigger tires, but as far as performance is concerned I believe I've got the perfect combination.