Watched a movie on it today during late afternoon. I had no eyestrain and sat through it comfortably. It is very bright though! I didn't notice at all when there was a bit of ambient lighting in the room from the daylight (even though there are shutters), but as soon as it got dark I noticed it was really bright (although my pupils react normally to even a smidge of natural light it doesn't matter how bright a screen or overhead light gets my pupils are always much larger than everyone around me). This makes sense considering that 5/100 brightnes was measured at 100 cd/m2 and peak brightness was measured at well over 300 cd/m2. Much like BenQ's VA panel monitors it doesn't wash out at min brightness setting and, setting aside complaints of over brightness at low ambient brightness, has similar comfort levels.
It is still early but I would reccomend this TV to anyone who has experience with BenQ VA monitors and finds them comfortable but is not bothered by ~100 cd/m2. My family found 0-5 brightness to be perfect for nightime viewing but they have normal eyes/brains.
I'm torn myself. The previous TV was much dimmer but gave me a bad eyegraine regardless (it had usual PWM) and was not usable at any time of day or ambient brightness. Since the X850E doesn't seem to have any intrinsically bad properties besides high brightness I could just wear one of my FL-41 tinted eyewear if I feel I need to.
I suspect it does not use aggressive dithering either as I'm pretty sure I would have felt that and would not have felt comfortable for as long as I did, but one test session definetely doesn't confirm anything. (I am using known good device PS3 for all my testing so dithering should not be coming from the device).
As for PQ the higher native contrast and deep blacks of the VA panel are really pulling their weight here and I don't think the picture suffers much from the lack of local dimming found on the more expensive models in this lineup.