I currently use a Sony KDL 32W706 which has response time of 15ms (apparently one of the quickest tvs?) and I can easily tell the difference between this and a Dell monitor (2ms response) when using it on a PC. Even my 60yo father who has never played a game in his life can tell the difference when just navigating his desktop as the cursor definitely feels slightly disconnected compared to a monitor, although completely usable.
Personally anything less than 30ms is perfectly usable for console gaming but for PC use, not just gaming, the closer to no delay the better.
Response time and 'input lag' are two very different things. An OLED TV has a 'response' time of less than 1ms (0.2ms with 0.0ms overshoot) - that beats most (if not all) monitors for PC's. Input Lag - on the 2017 models is around 21ms. Gaming Monitors rarely give their 'input lag' details as its all about the 'response time'
Input lag is a measurement of the delay between the time you enter a command on your keyboard, mouse, or controller, and the time it registers on your screen. A low input lag is crucial in "twitch" (time-sensitive) video games where fractions of a second matter.
Response Time is an indicator of how fast a pixel can go from black to white and back again on a particular monitor/screen. Response time isn't as important as input lag, although response times in excess of 5ms can sometimes produce images that feel blurry (that 'motion' blur that LCD TV's have) or have ghosting.
Many monitor's have less than 1 frame (16.666ms) of input lag and the best tend to be in the 0.5ms-10ms. It also depends on whether you have an IPS or TN monitor as IPS monitors tend to have around 5-10ms Response Times. TN monitors tend to be the best for input lag and response times but IPS panels tend to have the better and more accurate colours with wider viewing angles as well as often larger screens too.
If you care more about the image then about the responsiveness of your monitor, go with an IPS monitor; if you'd rather have better responsiveness, go with a TN monitor.
However with TV's, If you want a 4k HDR TV with the best response time AND decent input lag, go with an OLED. If you don't mind a tiny bit of 'motion' blur (as LCD's tend to have a 10-15ms response time) and on more of a budget, go with the LCD.
The difference between 15ms and 21ms is 6ms - that's 6 thousandths of a second! To put some perspective on it, it takes around 2tenths (200ms) to blink. The average 'human' response time to visual stimulus is 0.25s (250ms - 15 frames at 60fps). It can take just 0.15s to react to physical stimulus which is still 150ms (or around 9 frames at 60fps).
Lewis Hamilton has a 'reaction time' of around 200ms (
Is Your Reaction Time Faster Than Lewis Hamilton's? ) so quibbling over a few thousandths of second is ridiculous. No way can you feel the difference of 6ms Input Lag. I can appreciate that an image may not look as 'clean' because of a longer response time and can certainly tell the difference between 20ms and 60+ms but 6ms??