Is a wireless mouse less reactive than a classic mouse?

Wireless mice have several disadvantages for gaming, latency being one of them. They also have a nasty habit of dying just as you're about to get the game-winning kill. It may or may not be the biggest/only bottleneck to your gaming performance, but it's certainly true that more gaming mice exist that are wired than wireless.

As far as testing it goes, you could take a look at this article, which contains testing suggestions and tuning opportunities to measure the latency of you wireless mouse versus a wired one.