Ian and Remy,
Guys, another update...I thought I would max out the settings with the goal of achieving highest performance...then if I start running into problems I would dial things back a step at a time.
So here are my current applicable INETCFG.INI settings:
#Inetcfg: CURRENT DEFAULT MINIMUM MAXIMUM
keepalive 300 300 0 7800 KeepAlive (sec)
tcpswinsize 246723 32768 1024 246723 TCP SendWindow Size
tcprwinsize 246723 32768 1024 246723 TCP RecvWindow Size
udpswinsize 246723 41600 1024 246723 UDP SendWindow Size
udprwinsize 246723 41600 1024 246723 UDP RecvWindow Size
lingertime 120 120 0 65535 Linger Time (sec)
ipforward 0 0 0 1 IP Forwarding flag ON/OFF
timestmp 0 0 0 1 TCP TimeStamps ON/OFF
msl 30 30 1 16384 TCP MaxSegLifeTime (sec)
sack 1 0 0 1 Selective ACK ON/OFF
...the xxxwindsize have been set to MAX values.
I still need to research a bit to understand the impact of the following:
lingertime
ipforward
timestamp (I think this may be used by SACK, not sure though)
msl
....and drummroll for the results please!!!

1)
http://speedsmart.net/ => 87 Mb/s
2)
http://testmy.net => 40 Mb/s
3)
http://beta.speedtest.net => 91 Mb/s
4) FF download => 5000 KB/s, so roughly sustained 50 Mb/s
All in all, I would say that is basically what I'm seeing on my Winx boxes.