I have a small network with about ten users. All workstations flow into a Dell PowerConnect 3424 which then has a single link to a SonicWALL firewall and from there to a cable modem. More important than internet connectivity is speed between machines (specifically a Windows Server box on the LAN which everyone uses simultaneously). I believe the 3424 has gigabit connections, but they look like they're for stacking. 

Is there a way to test the speeds on the LAN to see where the speeds are at? 

Is there any low-hanging fruit insofar as increasing speeds?