Hi Andy, I checked with one of our engineers and he had to say this:
The 7982 by default has 20MHz of allocated bandwidth in the 2.4GHz band and 40MHz in the 5GHz band.
A second limitation is the client wireless card. If it's a single stream wireless card with the client that you're testing with then that throughput at 2GHz is reasonable.
A third limitation is contentious. If various APs clients are downloading content at the same time, then those 50Mbps get divided among all of the APs.
We don't suggest increasing the current bandwidth to 40MHz in 2.4GHz band as you may see more channel bandwidth allocated for throughput, but you run the risk of exposing, or further exposing, your network to interference.
One of the tools that you can use to see if the limit is between the AP/ZD is to run SpeedFlex, an embedded tool to get value of throughput between AP/ZD.
There are other factors that could be playing a role in your throughput like interference or RSSI strength, etc.
If you have a support contract and have a legitimate issue after reading this, then please open a case and we can investigate.