Recently purchased a 49XF9005 grade A refurb from Sony. The TV is as good as brand new. After a fair bit of picture setting adjustments (including trying out some other people's settings) I`ve found the picture quality to be generally very good.
However, after reading a few online reviews (which helped me choose this TV), I'm left slightly underwhelmed by the Freeview PQ. I didn't expect much from SD channels, but HD channels aren't quite as good as I expected. Sometimes the PQ is really good, depending on channel/content, but other times it seems to lack a bit of detail and appears slightly "soft". I understand that some programmes will look better than others, but my old Samsung 40" TV was far more consistent, and did a much better job upscaling SD channels. I decided to try my old Freeview recorder through a HDMI input. After a bit of adjustment I`ve got a noticeably better picture. Detail and sharpness are better. The difference isn't massive, but it's enough for me to appreciate that this TV is worth the £629 I paid for it. Shame that Sony don't seem to have done as good a job with the internal Freeview decoder as they could have done.
I`ve watched a few 4K Youtube videos, and the PQ really is excellent. The bottom line is that it's all very well having 4K screens, but with the majority of people still watching HD or even SD content I believe picture quality is somewhat compromised by having to upscale to the 4K screen, even on TVs that are supposed to have good picture processing.