If it's black and Netgear then it's the V2.
Wireless would be the most obvious cause of your problem, followed by overloaded test servers - but you've eliminated both of those. That leaves:
- a problem with your PC (interface drivers, TCP/IP settings etc)
- legitimate bandwidth "stealing" (e.g. another LAN user, P2P/Sky anytime running)
- non legitimate bandwidth "stealing" (e.g. malware, WIFI hijacking)
- a Sky network/routing problem
- a router fault
The first isn't likely to be TCP/IP settings as you're Vista but it could be your network card driver. Make sure you have the latest installed. If not that then maybe an obscure hardware fault but that's not likely.
The second is self evident - do you have anything like that running or have another user on the LAN?
Same with the third - turn off the wireless and run checks for malware
The fourth isn't likely so let's leave that for now.
The fifth, overheating can happen and sometimes routers just throw a wobbly. Power off your router and leave it off for 10 minutes. Power it back up and see if things have improved.
Edit: just noticed the contradiction between your Skyuser profile and your stats. It looks to me like you could be Connect not Base. Please confirm which. If Connect then you need to check your BT profile to see if that's the issue. Do you know how to?