How can I minimize the amount my router slows down my Internet connection speed?

Background

I'm working with what I assume is a pretty common Internet setup: a cable modem, a wireless router and a few Internet-connected devices. Lately, I've started being more demanding on my Internet connection, and noticed that using my router slows down my download speeds considerably.

I just kind of dealt with it until Zune Marketplace on the Xbox 360 told me that a movie was going to take well over ten hours to download, and I just didn't want to wait that long. Good little scientist that I am, I tried to reduce the problem down to one variable.

The test

As a control, I turned off all the devices in the house that use wireless Internet, and unplugged all the wired devices except for the Xbox. I also power-cycled both the modem and the router. I then tried to download the movie again, and was told that it would still take over ten hours.

Next, I unplugged the router, and connected the Xbox directly to the modem. The movie downloaded in just over one hour. As far as I can tell, this means that my ISP, other cable users near me, the remote servers, anything wireless-related and my machines' disk speeds can't be at fault.

A similar experiment that replaced the Xbox with a wired laptop produced similar results. To me, this says "the router is responsible for things taking around ten times longer to download."

My question

I'd still prefer to use the router for a few reasons:

1. it's a pain to connect and disconnect everything every time there's a big file to download


2. direct connection to the modem isn't good for security


3. only one machine can be connected directly to the modem at a time

What can I do to have fast connection speeds while still using the router? I don't mind turning other machines off, as long as I don't have to mess with power and ethernet cables.

EDIT :
After asking this followup question and then this one, I installed dd-wrt on my router, and I seem to be getting higher and more consistent speeds. Perhaps more importantly, my memory use is fairly constant. I know this isn't an answer — which is why I'm not posting it as an answer — but it is how I resolved the situation, and hopefully it'll be helpful for someone.

Answer

You can play with router settings to see if they make any difference. For example try enabling/disabling NAT/UPnP/Firewall on your device and check the speed each time you change something.

Although the router seems to be the problem according to your tests, I think, may be, it's not just router alone. It can also be related to Xbox services, i.e. your router works fine with other web sites/services but is having difficulty when dealing with Xbox (I had a similar issue and the only solution for me was to change the router because it was not supporting Xbox services). Have you taken any speed tests? Or download a big file (such as a linux distro) via torrent and see the effect of router on speeds.

Finally, try these tests with your router connected and see if it fails at any of them: http://www.microsoft.com/windows/using/tools/igd/default.mspx