Speed connection limit on VNC customized application

[C1-10P]

Dear all,

I'm writing this post in order to introduce an issue I'm encountering developing an UltraVNC application (I'm new in this forum and I hope this is the right section to do that. Sorry in advance if I made it wrong).

First of all,
a brief description on what I'm developing.
I have two pc, each one is equipped with an Gigabit Eth board Intel PRO1000,
computers are directly connected through a cross cable and a direct IP connection.
I'm working on the source code of UltraVNC in order to optimize (in my case it means make it as fast as possible) the transmission of a portion of the screen.
On the client side the connection status dialog shown the data receiving line speed (in Kb/s). Initially that value was limited at 20Mb/s and I noticed that this limit was set in the code (FdInStream class) in the function stopTiming.
I was wondering, why this limit was set? (this is my first maybe stupid question...).
Once I've removed that limit in any case the line speed is now reaching 40Mb/s that is quite quite slower than the theoretical 1Gb/s.
I know that this is a theoretical speed (1Gb/s) but I expect to be able to have faster transfer rate.
Is anyone able to give me a tip on this questions?

Thanks to all!