Most gaming monitors that have a 1 ms response time have a refresh rate of 144 Hz or higher. If your 5 ms monitor is a standard 60 Hz screen, then 5 ms is about as good as you can get. As far as being "fast enough" you also need to take into consideration what frame rate you're going to be gaming at as well as the type of game. If you're going to be gaming at 60 fps and not higher, then your current monitor would be just fine.