In short yes. To quote someone who can better explain.
My gear is setup correctly, that much I can be certain of. For what it's worth, I do receive my full throughout, in downloading and uploading, (980mbps down (ish), and 46mbps up (ish)). The issue I'm facing has to deal with how the TCP protocol works. In TCP network transfers, the client needs to send acknowledgements back to the server within a certain time frame acknowledging that it received the information sent to it, otherwise the server will reduce its transfer speed. If those acknowledgements are dropped (or in this case delayed as result of queueing due to competing network uploads) the download performance will suffer. Now, for UDP transfers, that's a different story. UDP will dump data down the line as fast as it will go and it doesn't care if all the packets make it to the client, so that's probably what you're seeing. If I was using UDP, I could saturate the download while saturating the upload without an issue, however, I'm using TCP. The TCP protocol needs around 30mbps in order to have enough bandwidth to send the acknowledgements back to the server fast enough to saturate a gigabit link (Assuming all of the connections between the client and server have adequate peering). If I have a competing upload occurring simultaneously, there's only about 15mbps (at most) of wiggle room until the line capacity is met and the network performance will suffer.