Great info there, I can add a few other pieces of info. If you want to do a lot of offroading, going with the lower rating gives you a softer sidewall.
C rated is lower than E and is a much softer ride - I have 2 sets of tires for my suburban (3/4 ton tow rig) and there is a noticeable difference. The E rated tires tow great, nice and tight, but feel like I'm driving on cobblestones. The C rated tires actually have a 'loose' feel like the front tires are floating, but wow! they are great for quiet drives and are very soft on even rough pavement. I would highly recommend load rating C unless you tow.
Everything has a tradeoff, I loved the C rated BFG AT/KO tires for my Jeep and will likely be getting the 315s for the Hummer when I wear out the current tires (I just checked, they are rated C). I will go with the C rated, since I can tow with the suburban.