Hi George,
The only Z-4000 rated at165 VA was the first run from March 1998. The ones from the second run on are rated 180 VA. I have both and they have 12 amp breakers.
If you are using the Z-4000 side receiver, it will shut down the transformer at with the least little short or spark extremely quick, which I use most of the time.
Using the Z-4000 without the side receiver you should be able to run up to 11 to 12 amps with no problem, at least I can. I just got a chance to make sure I was right by running 3 loops and 3 engines plus passenger cars on 1 TIU channel today without the side receiver.