I really like the Rancho setup; the one-piece subframe makes for a stout system, and the system also retains the factory steering geometry so handling is like stock (except for the higher center of gravity). The Rancho 5000 series shocks will give you a stiffer ride but still very tolerable and not bad at all, however you can get a much better ride with the adjustable 9000 series.
Going off road, you won't be able to take any jumps...lol...but for normal off-roading (rock crawling, mountain trailing, arroyo runs, etc.), the system works very well.
The power loss is really a function of the heavier mass of the 35 inch tires and aftermarket wheels, and so I definitely felt it with the 5.4L (more effort needed to get the big meats rolling) and so gas consumption was affected as well. I got about 12 mpg City driving and 14-15 mpg Highway if driven conservatively. I did slightly better with my 2011 5.0L Plat.