USB 2 will work just fine for Wifi dongles. You are not going to get anywhere near speeds high enough to saturate USB 2 with Wifi. With GigE adapters for USB 2

USB 2 will work just fine for Wifi dongles. You are not going to get anywhere near speeds high enough to saturate USB 2 with Wifi. With GigE adapters for USB 2 though, it is pretty bad.