Where do you get your facts & figures that most people prefer the IPS panels? If that's true, why do Samsung and Sony sell so many TVs? It all depends on your viewing habits. If you like the LD350C, then that's the one you should keep. It's rare to find a panel these days with good screen uniformity and it sounds like yours has few, if any, noticeable flaws.
As for SD, most HDTVs do a less than stellar job of displaying standard definition material, so I don't think I would use that as a criterion.
As for SD, most HDTVs do a less than stellar job of displaying standard definition material, so I don't think I would use that as a criterion.