They will fit, but do I want them?

I have been told that 285/70/17 Cooper Discoverer STT's will fit on my 08 TRD with 3" lift and AAL without rubbing or the need for trimming.
My question, is will I loose power, mess up my gear ratio, and stress the drive train?
I jumped two sizes on my last F-150 and felt that it was never the same. It seemed to loose power and torque. Granted the truck had 230K on it when I put them on, but it seemed to head downhill fast after going to the bigger tires.
I want these tires on black XD Revolvers but I don't want to end up regretting the decision. My other choice is Maxxis Bighorns or if the size is a real problem, I will probably go for some Big O Bigfoot XT's in 275/70/17.
Help me out please.

 

Had 285/75/16 Cooper STTs on my truck... I didn't need to trim with those, but I also think it's unrealistic to think you won't have to. (Plan for the worst, but hope for the best and all). Many people run that size with no adverse affects on the drive train.

I don't remember what it was like driving my truck without the bigger tires, but I never really noticed a considerable loss of power when I made the switch.

The STTs are fantastic! A bit noisy on the highway but that's because they're an MT. I regret not buying them again...

 

STTs seem like a good tire from what i've heard. the 285 should fit without much issue. I never really noticed a adverse effect on my truck from larger tires, except the steering got a little heavier from the wider offset wheels and of course a little MPG too.