The difference is substantial. Low ID takes a long time to get going and a lot of sharers won't be able to connect to you at all. It might be good for downloading very popular files.
I can only tell you what I did. I've got one computer with a Livebox router connected by ethernet cable (Ports eMule1 and eMule2) and also one wireless laptop which I had to configure separately (ports eMule3 and eMule4). This is because the two computers have different static IP addresses and TCP and SDT numbers. I'm using windows vista with no windows firewall and AVG anti virus.
I don't know why it hasn't worked for you. My only guess is the static IP address may be incorrect.
You can try repeating it and tweaking it.
1) Turn on eMule but don't connect (may have to disconnect server)
2) Change the TCP and UDP numbers to anything between 20000 and 70000 >Options> Connection
3) Switch off eMule and when you turn it back on you can see two new TCP and UDP numbers
4) Go to your router page and delete the eMule1 and eMule2 ports which you've previously configured.
5) Try to configure it again with the new TCP and UDP numbers and IP address.
Good luck