You're better off avoiding port 6881 if you can, that's the common port and so is usually the one that gets throttled by the ISPs. Better to use something in the late 49k (49056 for example).
You need to set this in your router and also within Az.
Limit your upload speed as well. I'm on 2Mb BB and my upload is set to 20k.
If you let me know what your upload speed is I'll give you pointers for the rest of the Az settings (or, better still, tell you how you can find them yourself
).