Need Info on Tires Quick!

So I've recently purchased a 2nd Gen Tacoma that came with 255/75/17s (KM1s) that were severely cupped. After several rounds with the stealership we've reached a point where they've offered to give me a set of 255/70/17 (Falken Rocky Mountains) used tires for free if I like them or we will start researching the trade value they'd give me on mine, the dealer cost price of new Cooper STTs, and what the difference in price would be.

My question is, does anyone have any advise on the size difference between 255/75/17s and 255/70/17s on stock suspension? Pictures would be helpful if you've got 'em too.

Thanks in advance guys,

RH01

P.S. If my search-fu was weak and you know of other threads, I apologize and appreciate the links!