No matter what other basic bolt ons you do nothing will give you as much of a kick as the 4.10s. Your call will feel like it has 360 hp not 260 once you put the gears in.
Lets see my car makes about 360hp, I have stage II cams all the bolt ons and 4.10 gears. I get 18mpg city/highway. All highway I'm 23+mpg. So not much changed from stock. Also I don't drive like a grandma.
EVERY gear pulls harder! Even 5th on the highway is sooo much better. After riding around with them for a year and a half, there is no way I could go back to the stock gears.
I have seen 24-25mpg with the 4.10's, babying the hell out of it driving 55-60mph for extended periods.
Overall, the mileage went down highway and up city by small amounts. Almost not even worth the discussion. It really all just evens out cause the gears help in pretty much all driving except constant highway cruise at 65+ when you start revving more than the stockers would have.