Seth, I don't think there is anything better than the Pios. They ARE the best at this size. When you talk about PJs, then some people will argue those are better, but we are talking 10x the price anyways, and a different size altogether.
At 50", the best would be the 111. However, the KRP500M for a lot less money, is the exact same thing minus a few side features (like extra hdmi I think), with the most important missing feature being the ControlCAL ISFccc (which lets you have SEPARATE calibrations for EVERY source, so that it is perfect for both day and night viewing).
However, you can still get around that, as here is a list of calibrators who can install that patch and then calibrate.
http://www.controlcal.com/forum/showthread.php?t=486
The problem is that these TVs are probably all gone now. Well, I'm sure there's a few around, you have to look. I do see the 60" version for sale.
Hm, the prices have seen to gone up on the KRPs. If they are close enough in pricing, I would go with the 111.