As with other 4K screens we've seen, when you're up-close the footage looks incredible. The pixels are so tightly packed together that the detail on offer really does look amazing.
As you step back from the TV though, the difference between 4K and 1080p is less noticeable. At around 4ft you can still resolve the extra detail, but move back to a more comfortable and normal viewing distance and it's much harder to tell.
At around 8ft I found it pretty difficult to see much difference at all between 1080p and 4K video. Sharp text on movie trailers stands out, but in standard video sequences at that kind of viewing distance it's not hugely apparent.
General picture quality
For general viewing the WT600B is a decent TV, but not as good as I'd expect for a set costing over three grand. Its colour performance is very good though -- landscape scenery looks excellent and subtle hues and textures such as skin tones are rendered with grace.
Its upscaling engine also does a decent job of both scaling up 1080p video to fill 4K's worth of pixels and tarting up all but the lowest bit rate channels on Freeview. On the whole though, standard definition content looks worse here than on a good 1080p screen, such as Panasonic's own ST60 model, and HD sources don't look any better on this display than they do on a native 1080p screen.
The WT600 seemed slightly worse than Sony's X9005 in terms of motion resolution, with more blurring on moving objects and sports footage. It's biggest failing though is its black levels. As you'd expect, this is most noticeable under low light conditions.
The native black levels of the panel aren't particularly good and a fair amount of cloudiness from the backlighting was visible in the four corners of the display. It has edge dimming, so it can reduce the intensity of the backlight, but Panasonic's dimming system on this set is just nowhere near as effective as Sony's dimming system on the X9005.
3D picture quality
Panasonic has opted to use active rather than passive 3D on this set, which isn't a clever move in my opinion. One of the big benefits of both the Sony and LG 4K TVs that I looked at recently was that even though they used the passive 3D system, the 4K resolution of their panels meant that they were still able to deliver crisp 1080p video to each eye without the flicker and heavy glasses associated with active 3D systems.
Panasonic includes two pairs of glasses with this TV, which is stingy given its extremely high price -- Samsung includes four active specs with its current 4K model. The same downsides associated with active 1080p systems are also evident here. The active glasses do cause some flicker on ambient light in your room, and this combined with their extra weight make them less comfortable to wear for the duration of a movie.
This set also suffers from crosstalk. Watching Hugo I often spotted ghosting creeping in. It was especially noticeable in scenes where there were brighter objects in the foreground against a darker background, such as on the boy's outstretched hand in the scene where he reaches for the wind-up mouse. The upshot is that this just doesn't compare favourably to Sony's and LG's 4K sets.
Sony strapped almost comically huge speakers to the sides of its KD-65X9005 and LG added a slick, motorised, drop-down soundbar to its 65LA970W. It's a shame then that Panasonic has stuck with pretty standard down firing stereo speakers on this model.
The results are distinctly average. The WT600 doesn't sound bad, but it doesn't sound good either. It lacks the full-bodied sonic prowess of Sony's X9005 and doesn't have the mid-range punch of LG's model. Dialogue still sounds crisp and clean, but it's crispy when dealing with high frequency sounds, and where you should hear bass rumbles you get flaccid, mid-range boominess instead. It's not terrible by any means, but it falls short of the solid audio performance its two peers that I tested recently.
It's great that the TX-L65WT600B has both HDMI and DisplayPort connections that can handle 4K video at up to 60 frames per second. It also has one of the slickest looking designs of any of the 4K sets on the market right now. For such an expensive TV, however, its black levels aren't very good, and that's exacerbated by its below-par edge dimming system. So, despite its HDMI 2.0 port, this is still not a tempting 4K buy.