5ms vs 2ms response time

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.