Just for future reference: If you have something to add, can you use the Edit button rather than making a new post? It's just easier for us to read it.
Ok, let me get this straight, this is the situation as I understand it, please correct me if I am wrong.
You have used several network cards on this machine, and all are experiencing the same issue with browsing speeds. In addition you have 2 laptops which connect wirelessly which can browse absolutely fine, the issue is specifically with this one machine.
Assuming the above is correct, here are a couple more questions and suggestions for you:
What brand of card are the other ones? Are they all unbranded cards?
Have you tried changing LAN port on your Router?
What happens if you connect the laptops via ethernet cable and turn off the wireless? Are they still unaffected?
Lastly, I have had a little bit of an idea.
Open an elevated command prompt (search for cmd in start menu>right click>open as administrator)
type "ipconfig /all" (no quotes) and press enter.
Find your network card, and make a note of the IP address under "Default Gateway" to obtain your Router's IP address (if you don't already know it)
type "ping <router's IP address>" (no quotes or <>'s)
post back the results.