You won't even notice the difference in 2ms and 5ms. Response time is how long it takes for the pixels to go to black and white and black again, and there is no way you can tell a difference by the naked eye.
The difference between 2 and 5 is virtually non existant. If you looked at a 2ms samsung and my 5ms lg you wouldnt be able to tell a difference in response time. Though you might notice the better color out of my lg
You really wanna know the difference? 3ms (5ms - 2ms = 3ms)
OT: You really won't see a difference. Some people claim they can see ghosting on a 5ms monitor/TV, but usually this is not the case. Save the money, I'd say.
Only time i'd start worrying about ghosting is 8ms up on 30" screens. If by some chance you see ghosting on a 5ms 24" you have one terrible monitor and shouldnt have gotten it anyway if you planned on playing video games :/
Either that or you're doped up or drunk and seeing double XD