How to get faster interet connection when behind a Netgear router

I have a good internet connection that can devliver about 93 Mbit/s traffic when a computer is directly plugged into the wall. When sitting behind my Netgear WGT624 v3 router my Windows XP computer can get about 45 Mbit/s and my linux computer can get about 60 Mbit/s. I'm guessing the difference of because Linux has a better TCP/IP implementation.

When tring to find my DNS problem I tried some different settings on my router. One setting gave me a speed effect:

 

I disabled the SPI Firewall (the settings is found on the WAN Setup page). Now this is probably not so good from a sercurity perspective...

After this setting my Windows computer increased about 5-10 Mbit/s . There was no clear increase for my Linux computer.