Try comparing the values from these "files" on the two kernels:

/proc/sys/net/ipv4/tcp_window_scaling
/proc/sys/net/ipv4/tcp_wmem


Then try toggling the value of /proc/sys/net/ipv4/tcp_window_scaling
(eg. just do echo 0 > /proc/sys/net/ipv4/tcp_window_scaling).

Or set it to 1, and change the other one to something like this:
echo "4096 16384 65536" > /proc/sys/net/ipv4/tcp_wmem

Experiment like that. If nothing much changes, then we can eliminate them
from the possible issues.

-ml