5ms and 2ms can be noticeable, but like said above, it's not going to really matter that much and it won't hinder your performance to have a 5ms monitor. It can help if you're some pro FPS gamer, but not significantly and other than that, you don't really need it.
I can't answer the question having never used a 2 ms monitor, but I will say games are definitely playable at higher response times. I have a Dell U2412M which has an 8ms response time and I play BF3, BF4, etc. every night. And kick butt doing it.