I think the flares have more to do w/ keeping rocks off the paint. Reason I say this is that I had an 00 w/ the 265/70/16 tire package and it had the running boards w/ the really small chrome strip over the wheel wells. The whole side of my truck was chipped from rocks getting past the flares. I now have an 02 w/ the limited/sport flares and the sport tube steps and same tires, this truck has almost no rock chips and I pretty much use them the same way. So it must be the flares keeping the rocks away as I am quite sure the tube steps do nothing.
I do think the running boards keep some of the winter road grime off the paint though.