With the setup you described, it seems very strange that you would get such a low throughput. This can be due to many things, however, to start off I would first attempt just a simple file transfer between the devices. Before using a benchmarking software, I suggest using a protocol such as FTP to transfer a large file and see what kinds of data rates you get. Don’t use Windows file sharing (SMB) as that will add a lot of overhead not giving you a proper result.
Additional things you can do include:
* Make sure that the cables are good
* Make sure none of the ports on the switch are configured to function at speeds of 100Mbps
* Take a look at the show interface output and make sure that the connections to the two PCs are indeed 1000 Mbps
* Check to see if there are any errors on the interfaces
Also, make sure you are using the right units for your tests. Some benchmarking software uses the MegaBytes per second rather than the more conventional Megabits. A 1 Gbps connection should provide you with speeds of at least 100 MegaBytes per second and should actually approach 120.
I hope this gives you a good start to continue your troubleshooting…