Mac Pro Late 2008 Slow Internet

Question

Hi,
I have a problem with my Mac Pro Late 2008, version 3.1.
I Have an High Speed internet connection 60mbps download and 10 mbps Upload.
I Have a Gigabit Routeur with a Gigabit Switch, and a proper cable setup made by a professional.
So here's the problem.
My Mac Pro cannot not acheive to get the 60 mbps speed in any way. the max that i can get is 20 mbps.
Here's what i tried :
With the same ethernet wire, i plug in 5 differents mac with different versions of OSX (2 Macbook Pro Retine, MacBook Pro 15", Mac Mini, MacBook Pro 13"), they all get the 60 MBPS speed.
With the same wire, i tried the 2 differents network plug on the mac pro.
All those test have been made with only this mac pro plugged into the Switch, so no other computer are using the Bandwidth. And the routeur reset to be sure it will give a new IP adress and forget all the other computer and devices.
I've tried different DNS on my mac pro, Google, OpenDNS (paid subscription), My internet provider.
I've reset the PRAM of my mac Pro
I've reset the SMS of my Mac Pro
I've done the test with 10.5.x, 10.6.x, 10.7.x, 10.8.x and 10.9.x
None of those procedure worked.
The only way that i finally get to have the 60MBPS is to plug the mac directly to the Cable Modem of my provider, without any routeur or switch, and you can understand, that's not a livable option.
So I don't what else to do, is anyone ad the same problem?
Here's the Specs :
  Nom du modèle :          Mac Pro
  Identifiant du modèle :          MacPro3,1
  Nom du processeur :          Quad-Core Intel Xeon
  Vitesse du processeur :          3 GHz
  Nombre de processeurs :          2
  Nombre total de cœurs :          8
  Cache de niveau 2 (par processeur) :          12 Mo
  Mémoire :          18 Go
  Vitesse du bus :          1,6 GHz
  Version de la ROM de démarrage :          MP31.006C.B05
  Version SMC (système) :          1.25f4
  Numéro de série (système) :          NQ******200
  UUID du matériel :          ****
<Edited By Host>

Answer 1

I'm using Speedtest.net to mesure my internet connection.
My local connection seem to run at gigabit speed. If i copy a very large file from my Mac pro to my MacMini Server, it take the same time as if i copy the same file from my macbook pro retina (wired connection of course, thunderbolt to ethernet adapater).
I don't really know how to mesure the Bandwidth, near changing the node.