tire diameter and engine power

I have a 96 4x4 Tacoma 2.7 litre 4 cyl with stock 15" rims. I am interested in switching to 16" rims so that I can get a taller, skinny tire 235/85/r16 that will give more clearance off road and perform better in snow. But I have heard that increasing tire diameter might mess with the engine power during hwy speed and throw it out of its optimum operating range. I have a manual transmission, so I'm not quite sure how it would be a problem. But, aside from the speedo being off, might this switch to a larger diameter rim and tire be a problem for the engine?

 

Nothing wrong with a 15" tire, they have 33x9.5 to 33x10.5