I too have thought about going with either 26 or 27's. Problem is the larger the tire the more weight there is to move them.
As with my Dodge dually, going from stock 17's to 19.5's, I lost 75 HP measured on a dyno. Needless to say, I'm back to stock size tires again.
I also think about clearances. I've read many times over about guys that get larger tires, then have rubbing issues, especially when turning or hitting bumps in a turn. Their remedy is then a lift kit. Seems like sometimes you have to change something else to fix the previous change. Just chasing that rabbit all over the place.
Sometimes it might be better to leave what works....alone.