Thanks Harry, actually the only ports you are supposed to forward for XBL are 3074 TCP/UDP and port 88 UDP. The other ports should be opened but not forwarded.
Well in my research when I was writing a sticky that's still in "beta" I found some conflicting info. Mainly, this is caused by a "better safe then sorry" approach to networking alot of support staff take. Or maybe it would better to call it the "Forward ALL the ports" ::insert meme here:: approach. :
Here is a example of the closest walk through I could find on Xbox's support page about Ports and how they relate to NAT. You will notice they say "Open the following ports", not foward, but open. However
here points to Portforward.com as it's suggested method and gives this specailized link:
http://portforward.com/english/applications/port_forwarding/XboxLive360/XboxLive360index.htm but that hasn't been updated in a while, so doesn't have the DGL-4500. You find it else where on the Portforward site but all it is are the instructions for the DGL-4300 renamed for the 4500, same pictures and everything. But I digress, my point is as you see in the Portforward instructions they show how to use "Gaming" which is a port forwarding method. At first I thought they just left out the LAN IP, but noticed that is blank until you fill out your IP at the start of the page.
Heres what I think happened. Xbox gets alot of calls on NAT and configuration issues about people's router that is outside their support. Their Reps just send people to Portforward. Someone complains, either a customer or some Xbox boss, that they should have something specfic for Xbox. Xbox asks Portforward.com to make a specific group for 360 users. Portforward just draws from it's current image and instruction stock but makes it specific to Xbox ports. Portforward asks Xbox what ports they use. Xbox sends a list of ports "used" or required to be open. Portforward...being named portforward and all, instead shows how to forward the port. Forwarding a port does have the effect of opening it, like taking the door of it's hinge has the effect of opening it, so it works. No one actually stops and reads what they are telling people to do. Other forums read Xbox's support site and portforward it, then see other random ports opening up to their Xbox and think they must have been missed, and add it to their walk through. And the whole thing grows off each other until the whole thing is more about instructions then logic.
Ok, I didn't mean to go so deep there so I will simplify it to some main points.
1. 3074 needs to be forwarded, and only when something is keeping UPnP from working correctly. All the other ports just need to be open.
2. Gamefuel is for traffic prioritization only, and does not effect NAT or really even lag for that matter. It only really helps if you get lag when other people use the network when your playing a game. Proof of concept: Set up your router with GF rules and get everything to work, disable GF, turn off Xbox, reboot router, turn on Xbox. Is NAT still open? I bet 100 nerd points it will be.
3. Take note that the first suggestions Xbox makes for NAT problems is let UPnP do it. This is the easiest, and in most cases, the best way, specifically with multiple Xboxs. If UPnP isn't working, I would try to find out why instead of bypassing it. JMHO.