Hi, i have just been down this path, I replaced my very worn 245/75's AT with 265/70 AT, there is very little difference in the gearing,(Google for a tyre size calculator and you will see), and I run 235/85MT's for off road. You will have to do the 'Camel Cut' which is no drama really, I havent bothered with stays or things, I don't believe that you need too.
It surprises alot of other drivers where tall and skinny will get you compared with much wider tyres, I reckon it all comes down to ground pressure.
Regards,
Jack

