If I understand correctly:
Realistically the maximum throughput I should expect from the USG1100 is around 2,000Mbps - 2,500Mbps (tcp)?
It depends on what kind of feature you had enabled between different networks. If you enabled all the UTM detections, the throughput will become lower.
For more information, you can refer to the data sheet here:
I also have some Zywall 310s. I see they have six cores like the USG1100. Is the difference between the 310 and the 1100 that the 1100 has a slightly faster processor?
USG series is bundled with UTM features by default which allow the users to have some additional advanced threat detection features. The Zywall series can do basic well known firewall functions. For more information about the Zywall series, you may refer to the data sheet below:
I was searching a solution for the same problem with USG110, really slow speeds for traffic between two VLAN's. As is turns out, one core can only handle, in my case, below 300mbit/s, all features disabled, while it was advertised 1600mbit/s in the datasheet. This means that any single user, copying files from another VLAN will never exceed those low speeds, no matter how many cores there are.
This is really misleading information and if this is the case, I believe I am going to switch to some other brand that has decent performance.
The speed advertised was for UDP
“Maximum throughput based on RFC 2544 (1,518-byte UDP packets).”
It may also be the case that UDP for a thread can go across cores were TCP can not.
I found this interesting knowledge base article on the Zyxel Europe Support site about throughput on various USG and Zywall devices.
It appears from the data in the article that the throughput between a Wan port and a Lan port varies based on the direction of traffic flow and Wan to Lan traffic throughput is significantly greater than the results for Lan to Lan or vlan to vlan posted in this thread.