I think this is a hard question to answer because you are using two different tire sizes...
I do not have a 5th Gen (yet) but concerning tires have some opinions....I have never owned a car - seriously. My first vehicle was a Chevy K5 Blazer that I wheeled the living crap out of....from there I owned nothing but Chevy 4x4 pickups, another K5, Jeep TJs, Jeep WJ, Jeep XJ, and a 3rd Gen 4runner.
When it comes to mud tires vs all terrains....if you do not regularly go in the mud, like REAL mud, you do not need mud tires. I grew up in OH/PA and mud was all the rage and I loved it (still would if I had it nearby and an old truck to beat on). But mud tires howl like a ticked off dog on the highway and can deafen your conversation or music, when they are new some may not seem that bad but eventually they will be noisy. they can also give you an annoying vibration as they wear, or steering wobble and balancing issues. They are not great in rain or snow compared to an AT. I mean like from my experiences no comparison, if you live somewhere it rains and snows alot, mud tires are NOT ideal. They do not turn as well nor stop as quickly, and often leaving a stop sign or traffic light if you are not in 4 wheel drive they will break lose unless you gently roll off the line. I do not remember exact mileage, but even beating on BFG ATs I could get 40-60k miles, with mud tires I bet I get half that. And yes they hurt mpg, if they are heavier, if they have more resistance due to gnarly tread, they can hurt gas mileage.
Now some people might blast me, but that is my experience in 25 years of driving only 4x4s. I've had the old school BFG MTs, Goodyear MTRs, Baja Claws, BFG KM2s....and yes I thought they were so cool, looked so sweet, and when I was younger I actually liked the howl going down the road. In the woods they were awesome, and on rocks they do well.
BUT in my 40s now I actually prefer ATs and next time I am slapping on tires I want to try the more mild ATs like perhaps the Toyo. I have Fun Countrys now and they are ok, but I am sure Toyos will be quieter and maybe better mpg. The new BFG ATs look nice too. Lots of options.
Mud tires look so bad a$$...and I still rubber neck when a nice lifted 4x4 with mud tires passes me, and the sound of their tires gives me a good smile. But these days I want a mild AT that lasts twice as long, is better on the highway, in the rain, and the snow...and can still do rocks and light mud quite well.
Whether you save money on gas mileage or not, you most certainly will have much longer tire life with a good all terrain hence saving lots of money long term with a vehicle you might keep forever like a Toyota.
