In regards to the gearing change, I'm thinking of doing the same thing for my E350 with 5.4l. My main motivation is to keep the van from downshifting out of OD so often. It seems like at cruise my van is below the power band, and a change in axle ratio would help out the big girl. Did you notice the same problem and was there an improvement with the gear change?
I think the gearing change was worth it. Before, the van felt heavier after going to a 285/75. Now, there is a little more pep (if you can call an E350 peppy). I notice it in smoother/more fluid shifts. I probably notice it most at lower speeds, but there is an improvement up to about 65mph. Around 65, the benefit isn't as noticeable. I didn't really have a problem with it dropping out of OD at highway speeds on flat stuff and I usually flip OD off on steeper hills where this would be a problem. At high speeds (above 75) I'm noticing decreased performance - slight, but noticeable. Luckily, I rarely dive 80+... but driving out I70 in Utah, trying to hold 85, the van seemed to struggle a bit more.
Overall, however, it is more of an improvement that I thought it would be and I'm glad I did it.