I've got a 72" Eagle plow on my 800. It handles this blade width well and can push an amazing amount of snow. I think that summer mud holes would be much more load on your drive train because, in winter, you just don't have the same amount of grip on any surface. I'm on my original belt from 2011.
I can recommend the 72" blade width, especially if you're plowing around curves like I do clearing off a skating pond. I cannot recommend the Eagle plow however as it has "uncurled" quite a bit at both ends (the wear bar is visibly pushed back >1" at both ends with respect to the center of the blade). This is not from hitting curbs or manhole covers, just from "normal" use. Granted, as the winter progresses the old windrows at the edge of the pond or driveway, where the blade tips hit, get pretty hard... but that's what a snowplow should be made to handle. With less cantilevered length, a 66" or 60" blade would be stiffer and less likely to deform.