After many hours of struggle to get my new cable connection to perform at top speed thru my Endian Firewall (Linux kernel 2.6.x), I finally got it to work after stumbling upon this very nice little Tuning Guide.

To get my Videotron TGV50 to run at 55MBPs, I added/modified the following lines of the file /etc/sysctl.conf

net.ipv4.tcp_window_scaling = 1
net.ipv4.tcp_ecn = 1
net.core.rmem_max = 16777216
net.core.wmem_max = 16777216
net.ipv4.tcp_rmem = 4096 87380 16777216
net.ipv4.tcp_wmem = 4096 65536 16777216

then saved, ran the command
sysctl -p

and rebooted.

With the same router using the original configuration, I could only achieve 32MBPs. A gain above 70%!

I created this thread to share this little success story hoping it helps a few of you out there!