UL Benchmarks reports they're working on a PCI Express 4.0 test for 3DMark. This new benchmark is expected to be out later this summer.
3DMark PCI Express feature test
PCI Express (PCIe) is a standard interface that provides high-bandwidth communication between devices in a computer. New PCI Express 4.0 interfaces provide up to twice the bandwidth of PCI Express 3.0. With more bandwidth, games can transfer more data, reduce loading times, and support more complex scenes.
3DMark feature tests are specialized tests for specific technologies. The 3DMark PCI Express feature test is designed to measure the bandwidth available to your GPU over the PCIe interface. It will help you compare bandwidth across PCIe generations with a test that's quick and easy to use.
The PCI Express feature test will be coming to 3DMark this summer. It will be available as a free update for 3DMark Advanced Edition and for 3DMark Professional Edition customers with a valid annual license.