For Sony TV, in my experience December is a good month to buy. During their Christmas promos, they would usually drop the price of their premium models (you know, the ones with the excellent panels; I don't care much about "smart features"). Sometimes this is not immediately obvious, since the price drop of the unit is offset by bundling lots of "freebies" (which you know you are also paying for). But at the end of the day, you can sell off the bundled stuff, and end up with a low net price for the unit alone. And besides, I find it easier to ask for discounts during holiday season.
That's what I did 2 years ago with the Bravia W900 Triluminos top-of-the-line (for non-4K models). After selling the bundled HT, PS2, and digicam, I ended up spending just a few thousands more than if I bought W800 series. Then a couple of months later, they replaced the model with a (usual) super expensive flagship model.
Now if we are referring to 4K TV, regardless of brand, the worst time to buy a 4K TV is NOW. Not a lot of 4K material is available, plus 4K TVs with good upscalers are expensive, so there's a chance you would end up liking the picture quality of your 1080p videos on your existing Full HD TV than if you upscale it on a "regular" 4K TV.
