How to measure actual USB3 port speed?

Not all USB3 ports are created equal.

I have a friend who develops embedded hardware that interfaces with USB chipsets. He told me that most USB chipsets that are slightly faster than USB2 (480 Mbit/s) are labeled as USB3 even if they fall far short of the 5Gb/s theoretical limit.

I'd like to transfer uncompressed video over USB3. According to http://en.wikipedia.org/wiki/Uncompressed_video#Storage_and_Data_Rates_for_Uncompressed_Video 24bit @ 1080i @ 30fps requires 1.39Gbps. How do I measure the actual transfer speed supported by a USB3 port?

Most manufacturers don't mention the actual USB3 speed and I don't have anything to connect to the USB3 port that will transfer at speeds even close to the theoretical speed of 5Gbps. I will later on, when I get the live uncompressed video stream, but I'd like to test the USB3 port before buying this expensive video streaming equipment.

Most tech sites (annandtech, techreport, etc) include USB comparisons in their motherboard reviews. For example techreport in this review uses CystalDiskMark to compare read/write speed of various controllers. They use an external drive to test the USB speed. From the testing methods page:

The Force GT 120GB SSD was used as the system drive for all tests. The Samsung 830 Series 256GB was connected as secondary storage to test Serial ATA and USB performance, the latter through a USAP-compatible Thermaltake BlacX 5G docking station. With RoboBench, we used the Samsung SSD as the source drive and the OCZ RevoDrive 3 X2 240GB as the destination for the read speed tests. Those roles were reversed for RoboBench's write speed tests.

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