"InBrowser message" bandwidth hidden throttle ?

[zapper]

We are operating a network using Firstspot 6.09 Advanced edition.
Our hardware is a Dell Optiplex 760 , Intel Core2Duo E8400 at 3 GHz , 2 Gb DDR2 , 2 Gigabit LAN , Windows 7 Pro 32 Bit .

Our issue is the overall drop in speed for internet traffic experienced by our users when we are activating the "In Browser message" option (top banner).

Our Gigabit WAN connection (Internet side) is working at more than 160 Mbps full duplex (160 Mbps download and 160 Mbps upload to internet) when we are NOT using this option.This is the full sped from our internet provider contract.
But when we engage the "Top banner" mode or even the "Global message" text option , the overall speed is dropping to no more than 10 Mbps download and 1.5 Mbps upload
We have tested this issue by disconnecting the whole "Visitor" network and used just one laptop-client at that interface , with no bandwithh throttle .
Thsi behavior appears on many different server machines we tried , regardless of configurations.
For URL test we have used the speedtest.net test with the same remote server every time.

We are NOT using any kind of "bandwidth throttling" in Firstspot.
We have tested also Firstspot 7.11 Trial with same results: 10-11 Mbps download and 1.5 Mbps upload

Can you help us to increase the internet speed for the "In browser message" situation ?