At 275/65/18, you are 32" tall, which is going to rub quite a bit when off roading. A 31.5" tire (285/60/18) has proven to be as tall as you can go with only slight or mild rubbing when stuffed (full compression). If you have rear air conditioning, this is something to seriously consider, because the refrigerant lines run in an area that the right rear tire makes contact with.
Also, if you need to fit tire chains due to your location or use, start thinking 31", such as a 275/60/18, which is harder to find.
More on tire options here:
http://blog.nextstepdesigns.com/?p=46