I was thinking about that S-135 and S-110 axle thing. Dana gives some pretty in-depth specs on the Roadranger site about the S-110 series axles but very little on the S-135. Seems like the 110 series is the better axle choice to me, despite the ring gear size difference.

Visteon lists all the 10.5" axles, SRW and DRW, as 9750 lbs on their website and the same torque and GCWR specs as well. Sounds like the rating differences Ford applies to them are due more to differences in the rest of the rear suspension of the different models of trucks, probably mostly the springs, but the carrier info you stated is interesting too.

Dana rates the Dana80 in general at 11,000 or 11,500 lbs on thier website. Most of the different truck manufacturers using seem to rate it differently once it's in the truck though.

Thanks for taking the time to post up the details you found, it does help clear up some of the mysteries at least.