Depending on how deep your pockets are, I have heard plenty about the XBR8, which is Sony's first foray into Local Dimming LED backlight LCDs. The blacks are said to be the deepest of any LCD ever (including Samsungs LED LCD, the 81F series) and could come as close to a Kuro as you can possibly hope that an LCD ever could come.
These will not be cheap obviously.
In terms of the XBR6, I expect the requisite improved black level, improved contrast ratio, improved processing, improved styling (highly subjective) that you would expect with any new iteration of a television line. You can probably also throw in improved 120hz Motion processing as well.
Whether these additions, barring any new must have features that I am not aware of, will make it worth the price of admission, compared to a discounted XBR4, only time will tell.
I am curious to lay eyes on it, and especially the XBR8, when they hit stores.
Has anyone heard anything about the improvements for the XBR 6 line coming out by Sony ? I have to say, the XBR 4&5 impressed the hell out of me and I am simply waiting in the bushes to pick up a 52" in August...unless anyone here convinces me otherwise.