Impact of download speed on slower systems

[pvandam]

I recently have upgraded my internet connection speed to 120Mbps and my provider is capable of delivering that speed.
On my desktop (Core i7), when I use SABnzbd 0.6 Final, the download speed is pretty stable and reaches about 14.5MB/s (116 Mbps, so close to fully utilizing the internet connection bandwidth).
This means that factors like router, Firewall and AV software all don't seem to have a lot of impact on my download performance.

On my server however (Atom 525, WHS 2011) the speed is lower and more variable (between 8MB/S and 11MB/s).

As the network and desktop setup with SABnzbd prove that I can have the full bandwidth download, I've started looking at the server itself.
The server can copy files to and from the desktop at 90MB/s (bascially the maximum speed of my HDD's), sometimes dropping to 50-60MB/s.
The Server does not have AV software and testing with or without firewall doesn't make a difference.
On the Server I run SABnzbd as a service, and the corresponding process utilizes between 15 and 25% of processor capacity when it is busy downloading (distributed over 4 cores)
I have followed the guidance in http://wiki.sabnzbd.org/highspeed-downloading and set Article Cache to 120M and lowered my server connections to 20.
Some TCP optimizations and making sure I have the latest network driver on the server were the last things I tried to further improve the Server's download speed.

My goal is obviously to use the Server for downloading and get it to a state where I can have the same download performance as on my desktop with SABNZBD.

Hoping to find some throughts from people who have experienced the same.
Is this Atom 525 realy to slow to be able to reach 14,5MB/s with SABnzbd? What would be the real bottleneck and is there anything else I could to to futher optimize this setup?
I'm currently stuck at around 9MB/s, which is like almost utilizing an 80Mbps line and I know that is already pretty good, just trying to get to the max and I know SABnzbd can do it perfectly.

[shypike]

SABnzbd is a rather CPU-hungry program.
I don't think you'll get it much faster than this.
We will be looking at some improvement in the future,
but we're very much limited by the programming language (Python).

[daniel_owen_uk]

Does the atom have a gigabit network port?

[pvandam]

Does the atom have a gigabit network port?

Yes, it does and it performs well copying files. The values I reported above (90 MB /s and 50-60MB/s) are way above a 100Mbps network card.
The maximum speed for a 100Mbps card would be around 12,5MB/s.

[pvandam]

SABnzbd is a rather CPU-hungry program.
I don't think you'll get it much faster than this.
We will be looking at some improvement in the future,
but we're very much limited by the programming language (Python).

Thanks shypike for your answer. It's good to know that I should not be looking into further finetuning.
Apperently the combination of the Atom 525 and the Python language don't get it to it's optimal state.

Hoping for some improvements in the furture, I really like SABnzbd for it's web UI, capability to run as a service (on a server) and remote accessability features.