Originally Posted by toncij
Yes. Overshoot for one. It's awful. Keep it at 144 max. (check TFTCentral for details).
are you sure its that
TFT Central doesnt have a XB271HU review, but they have a PG279Q one and it says:
One of the most important tests for an overclocked refresh rate is whether it can support that without dropping frames. We tested the screen using the BlurBusters.com frame skipping test and were very pleased to see that no frames were dropped at all, even at the maximum 165Hz refresh rate. This overclocking seemed to work very well, at least from our test system and we were impressed.
One area which wasn't quite as good though was the response times. We tested these again at 165Hz and compared them to our measurements we had taken at the optimum 144Hz refresh rate earlier. As a reminder, we found that as you increase the refresh rate from 60Hz to 144Hz, the response times improved as you went. The response times and overdrive impulse are dynamically controlled by the G-sync module it seems, and influenced by the active refresh rate. We hoped for a further improvement with the boost to 165Hz but actually the opposite was the case.
The response times were slightly slower overall at 165Hz than they had been at 144Hz. The average G2G was now 6.0ms instead of 5.2ms at 144Hz. This translated to a small amount of increased motion blur, but we're talking very very slight. This is arguably offset anyway by the slight improvement in motion clarity brought about by the higher frame rate / higher refresh rate.
If we look specifically at one measurement, from 0 - 150 you can see what is happening more clearly. The above graph represents a change in brightness from black (0) along the bottom flat green line, to middle grey (150) along the upper flat(ish) green line. Those are the two shades being compared, 0 and 150. The time it takes to change between the two shades is the response time. We take an allowance of 10% on either side, so we measure the response time from the point where there has been a 10% change already, to where it reaches 90% of the desired brightness. This is a standard measurement process for panel manufacturers when measuring pixel response times. So the horizontal blue and red lines represent those points. The blue horizontal line representing the brightness 10% in to the change from black (0) to grey (150), and the red line representing the brightness when it reaches 90% of the desired shade. We then measure the distance between those two lines, shown by the two vertical lines and that is the response time.
At 144Hz as shown above, this particular transition from 0-150 has a response time of 5.3ms.
If we run the exact same test but at a 165Hz refresh rate the graph changes a bit. You can see that the distance between the two vertical lines is now greater, and this represents a response time of 10.8ms now.
The reason for the difference seems to be down to the overdrive impulse and the way it is being applied. You can see that at 165Hz the brightness change tales off when it reached about 80% of the desired brightness and then takes a bit longer to reach that 90% threshold, whereas at 144Hz is pushed the brightness change more quickly. This tailing off the overdrive impulse is designed to avoid overshooting the required brightness level, which in itself causes problems with trails, ghosting and dark/pale overshoot artefacts if not done. So it seems that at the overclocked 165Hz refresh rate the overdrive impulse is not being applied as aggressively and so response times are a little slower.
We should point out that this is hardly a big change, and as we say, the slightly slower response times are probably offset in actual performance by the slightly improved motion clarity from the higher refresh rate. Try the screen out with and without overclocking enabled and see how you get on. The main take-away here is that the 165Hz support is not really a great improvement over 144Hz in our opinion. You'll probably struggle to reach that kind of frame rate anyway, and if you do, the extra 21Hz is hardly worth it when you take into account the slightly slower response times as well. The screen is just as good at 144Hz so don't worry if you're an AMD user or someone with an NVIDIA card less than a GTX960, you aren't missing much.
one thing why I am interested in 160 or 165Hz is that Ive heard a few people claim that @ 160/165Hz they dont get the "shifted vertical line issue", whereas @ 144 they do
if that is indeed so then I could prefer running 160/165 instead of dealing with Acer repair services for the new fw upgrade (that is bound to be a long headache)