When it comes to a mouse, there are a couple things you need to understand.
1. Higher response time is Always better. For that reason alone a gaming mouse is better.
2. If you have poor mouse control, you want a lower sensitivity to make up for mistakes in hand movement.
3. If you have very precise mouse control, you may want a higher sensitivity to exploit this with precise twitches and etc. HOWEVER, if you are perfectly using your sensitivity stay with it.
...And something weird with warband that you may want to know. This may be anecdotal, but every player I have met has agreed on something weird. When you have a higher mouse sensitivity [ say, max in game sensitivity] your swings are faster. No idea what causes it, except for the funky way the game engine works or something. Could be completely wrong and I hope to god we are.