|I hate to be disagreeable phil22 but I can't agree when you say "The other run-of-mill ones (Netgear, D-Link, Linksys, Belkin etc) have a life of only a few years"|
I'm running a Linksys WRT54GL (with Tomato firmware) in my home and have been for around 7 years now. The original release date of this piece of hardware was somewhere around 2002/2003 and there are actually quite a few of them still running out there. FWIW, I did shut off the wireless on it when I bought a dual radio Access Point that I plugged into the router. The old girl is only G/B and single band (radio).
I've had devices that were brand new and didn't work out of the box and others that worked for years and years and years. Unless you get some major malfunction, devices like a SOHO Router or a switch should run basically forever.
While I wouldn't rule out a hardware issue regarding the OP's question, I would start troubleshooting elsewhere.
The OP states there are 7 people on this LAN two of which game a lot. My big question is, are any of the other 5 (and/or the 2 gamers) also downloading a lot files or streaming video when you notice this slow down?
If two or three other LAN users are streaming video (ie: Netflix or something like that) or downloading big files at the same time you're testing or gaming, that would explain the loss of bandwidth.
Troubleshooting is fairly simple. Disconnect everybody with a wired connection (except the test machine) and deny service to all wireless clients and then run a bandwidth test. Then enable/reconnect everybody and test again a few hours later (gives them time to get back to doing what they were). Then test again the following day. If there's no difference with only the one machine (again, a wired connection) doing the bandwidth test as versus all clients connected, then chances are you may be having provider issues or hardware issues.
If however, the bandwidth is as good as can be expected, then the issue is other users on the LAN hogging up the bandwidth. Video streaming and downloading are very bandwidth intense. I'm a gamer myself and I can normally tell when my wife fires up a video or Netflix when I'm gaming as my game gets a little choppy.
If it is a case of bandwidth saturation you have options. If your present router is able to do bandwidth limiting you could choke the others who are sucking it all up. Or you could get a bigger package from your provider (if that's an option, it's not where I live).
It matters not how straight the gate,
How charged with punishments the scroll,
I am the master of my fate;
I am the captain of my soul.