Other things to consider is what you have for a drive train. A stock 2.6 with an auto is going to lose a fair amount of pep and fuel economy pulling those taller tires. The stick is not as bad and the V6 should be just fine.
Kevin C
It depends on what kind of rims your putting them on also. I moved from 235/75 on the steel rims to 31x10.5 on the LS Alloys and if anything saw an improvement. I can't speak for the auto, but with the stick and 31s on alloys you won't see any drastic change. On the other hand steel rims are heavier, and you might get some kind of slight loss then.
My experiance was similar in that wider rims did help reduce rolling rsistance, and switching over to aluminum rims reduces the weight penalty of going to larger tires but I found it was a much smaller effect compared to the change in effective gearing.
Also its hard to get a set of large tires that have low rolling resistance, I really wish the rolling resistance was publised.
My Raider is due for a new set of tires and I would like to make as good a choice as possible (I'm going with 31x10.5'x15"). I have cosidered using another set of BFG AT's. My set are the pre KO version, I am curious how much better the KO's are?
In my experiance the BFG's are a great off road street tire but not so good in the snow. I want better snow performance and lower rolling resistance than what I currently have.
Getting back on track.....
When you go to larger, wider tires; reducing the camber angle to as close to 0? helps to reduce rolling resistance and promotes longer tire life.
Kevin C