power/tire size/mileage

just wondering what the biggest tire i could go with on a stock 09 tacoma 4x4? was thinking 265,75 16. i will be puting a leveling kit in as well also how much will this effect my gas milage and power? also would regearing help with this ? if it does how much will it help and whats it gunna cost me?

 

I have the TSB rear and 5100s all around with the fronts set at .8" and I run the 265/75-16 Michelin MS2s. My mileage has dropped less than 0.1mpg once I factored in the different rolling diameter.
The tires are not Load Range E, so they are not as heavy as some of them out there. They also are not an aggressive tread.