I think GBE is related to Newark connectivity. It's not what we care about.
Please check next to the PCIe slots to see if it says anything on the motherboard. It should say something like "PCIe 2.0" or something. Try this if you don't find anything: https://superuser.com/questions/8721...our-system-has
The biggest problem should be your space. As Cortb said, you should try measuring or finding the manufacturer's website and check the maximum size of card that supports. Usually they'll tell you something like "Supports cards up to 280mm x 150mm" or something similar.
Try finding that information and write back. Without that we are just guessing.