While the inflated specs mean nothing, the true native contrast ratios never lie. I've seen dlp's, lcd's, lcos, and crt. The numbers in the specs sheet will inflate the contrast ratios for dlp's and lcd's. The JVC lcos is actually a real number that can be obtained with accurate color.
Generally dlp's in this price range will have a native contrast ratio of 2-4000:1. Lcd's actually have passed dlp's and can reach as high as 6000:1. Lcos under most viewing conditions are around 15-20,000:1, but if you have either a small screen or one with gain, the advertised 50:000:1 is real.
The adaptive irises can help a lot but there are many forum members that have also seen all of the display technologies and are hooked on the JVC's. I think natural yet dynamic is a great way to describe the JVC's. Just ask the former CRT users!
Of course, there is the whole ansi contrast/bright scene contrast to consider that will complicate the comparisons. That's a number that doesn't lie either. Dlp's are best, followed by lcd, then lcos last.
So long story short: To most the JVC is a significant upgrade from the Panasonic. I'm sure many have gone from a Panasonic to the JVC but I'm sure very few have gone from the JVC to the Panasonic.