Try comparing your WAN address (the 80.223.42.x one) with the one on the NATCheck page. Do they match? If they do, good. If not, then reply here again.
You mention that your router uses "dynamic NAT". I assume you mean that you are talking about DCHP, which means that your LAN ip addresses may change with reboots of your computer. You should enable a static IP for your computer. I can give you exact intructions on this, due to the differences in the terms used in different routers. Basically, you have to assign your com an IP like 10.0.0.50, a IP address that is out of your DHCP range. (The alternative is turning off DCHP altogether. You can then assign your com the IP add 10.0.0.2, 10.0.0.3, and so on for your other computers.)
ID caan be set to anything. Your private and public port should be set to 6881, your host IP adress should be the one you just assigned to your com (10.0.0.50 or 10.0.0.2) Port type should be set to TCP.
After all this, test your setup with NATCheck.
BTW, if you're wondering why downloads on certain torrents can be faster or slower, it mainly has to do with the number of seeders and leeches present. If also has to do with the number of people who have properly configured systems (as in they allow incoming connections. AKA "active" computers). Only these people can connect to "passive" computers (disallowing incoming connections).So less people can connect to you, so less chance of finding fast connections. You can get a more concise explaination here:
http://bt.degreez.net/firewalled.html