It is most likely that your bottleneck is not your router, but your ISP connection. What is your upload speed? (You can test on Speedtest.net).
I have an ethernet hub nearby my media station, so I perfer not to use the wireless. That decision is more for reliability than speed. If you have the luxury of access to both, I would definitely plug it in.
If it helps, I have tested my connection with thru wireless (on my Netgear wnr-2000) and the performance was just as good as hardwire.
I also used to have horrible performance when streaming HD conten.
No, it wasn't my router, but my ISP connection speeds at both ends. Unfortunately, depending on where you are, sometimes there is no alternative--and that was my case. On the receiving (Slingbox viewing) side, my ISP was providing fast speeds; however, on the sending (Home) side, my ISP had horrible, horrible speed.
Finally they were able to upgrade my area and I got the upgrade in speed and now the streaming of HD content was very much viewable. I wsa very happy.
I, too, am into the fastest speeds possible so even at home, my setup is such that I have switches at strategic locations to allow for hard-wired connections, instead of wireless. I' into HD and 3D, so I want the fastest streaming possible and that's why I opt for wired.