Well, after a few more days of fiddling with the 844's settings, I've come up with a picture that I'm quite satisfied with. At the risk of being banished from the AVS Forum, I have to say that my new settings appear close to the Sharp's 'dynamic' mode (yes, I'm sure my visual judgement is no better than that of a moth approaching a bright flame). The settings are not perfect, but they seem to do well in the very bright room where the TV is located. The 1080p/i content, to me, looks very good and, surprisingly, the 480i material is not looking too bad either. So, the TV's a keeper for me. I appreciate all the comments posted in response to my earlier inquiry.
I now have the monster attached to the wall using a Sanus XF228. Installation of the bracket and mounting of the TV was a breeze, although I am still dumbfounded that all this weight is supported by four 3.5 inch lag bolts. My primary viewing position is 15 to 20 feet from the TV. The screen size (and semi-matte finish which reduces reflections in the bright room) make viewing a pleasure.
I found the Sharp's internal speakers to be particularly inadequate, so I purchased a Yamaha YAS-101 sound bar and am very happy with the improved sound. I do have a Definitive Technology 5.1 system for movie viewing but I usually use a TV's speakers for the day to day stuff (e.g., news, etc). The Yamaha sound bar is a well-thought out device that works seamlessly with the Sharp.
I have to stick with my cable provider for the time being and unfortunately they still have a lot of SD content. While I know I'm asking to put lipstick on a pig, I am interested in any video processing equipment that does a good job squeezing out the best possible picture from an SD feed. My older (and smaller) XBR9 Sony did a really nice job. Anything i can do to further improve the SD on this much, much larger Sharp would be helpful.