In addition to Bob's comments, just having a Gigabit ports does not necessarily mean you can transfer data across those ports at those speeds for a number of reasons. A better measure would be to verify the actual data transfer rate to between devices using those ports.
One easy test would be to use a pair of Macs (or PCs, or combinations of both) with a command-line utility like iPerf or its graphical interface cousin: jPerf.
You can find a Mac-version of jPerf here: jPerf for OS X
iPerf/jPerf works in a server-client fashion. You would configure one network client as the server and another as a client. You can then run a series of tests to verify the actual data transfer rate. You can then test how changing parameters, like the MTU value, affects this rate.