This server seems to be getting laggier and laggier. When GO wasn't as popular and the server wasn't that full things seemed relatively smooth. Now that the server is nearly always full the game becomes a slideshow. This is not a client side issue, my machine is perfectly capable of handling the game and I even have the graphics turned down just to eliminate that variable. Perhaps consider reducing the player count.
my specs for reference:
Detroit - 35Mbs line
Radeon HD 5870
AMD Phenom II X4 965 3.4GHz
8 GB ram
I've recently started playing more of Valve's official Arm Race because the servers run much smoother and I've also returned to your source GG servers.