Cisco/Linksys EA6500 is sloooow

We just opened our office, and got a 100Mbit fiber connection, and another 50Mbit cable connection (for 2 separate networks in the office). When we connect a laptop or use an Apple Time Machine on either WLAN connection, we see speeds approximately equal to what we are supposed to get. However, when we connect the Cisco EA6500 to either connection, we get only about 20Mbits download (but 20 mbit upload!) on either the internal LAN connection or using WiFi.

This is the second 6500 we got - what could we be doing wrong? We do forward ports - would that slow it down so much?

Thanks much for any help!