Self Explanatory.
TN panels have no problem, generally, reaching a rated 1ms time.
The lowest I've seen on IPS is 4ms rated.
Let's discuss
Doesn't really matter so long as it isn't above like 20ms like some TVs
It really is game dependent I would not want to play a twitch shooter with a monitor that does 15-20ms but if i'm playing an RTS then that 15-20 ms response is not really that horrible of a response time.
It is all task dependent which is why there is no one best monitor.
I have two tvs that I have played pc games on and console games on and I believe the response time is 8 ms but it could be higher and with that said I have had no complaints by others and I can't complain either.
You talking about pixel transient time or the processing input lag?
Pixel transient time is something like 1ms while input lag is generally anywhere from 10ms to 70ms.
If i can notice it, then its too much. I have a TV with MASSIVE lag. (50+ms) if you are serious about competitive games then id stay at or below 5ms.
I can notice the lag on my TV when I plug my laptop into it, but I can't tell the difference on my lovely AH-VA/IPS monitor, even though they're supposedly slower than TNs.
Although actually, Wendell did some testing and found that a 4K samsung TN monitor was slower than a certain IPS he was testing it with...