file copy speed extreme slowdown after that nic card has ICS enabled

2 windows 7 PC involved direct conneted to each other gigabyte nic cards.
I booted up win7 on the ubuntu PC (dual boots)

And did a large file copy from client win7 to other win7 that has internet. Results were close to 70 MB/sec

Now it is terrible slow AFTER I enbled ICS on that nic card to share the internet to other win7 PC.

So please explain to me how doing that would kill file copy that bad.
Went from 70 to 10 MB/sec

Ok, turned off ICS sharing and verified it was not running under services.
LAN copy speed back up high again, about 100MB/sec

So why is this happening?

buggy ICS IMO.
If you hate someone, and want to slow down their LAN speeds, tell them to use ICS.

Is there another way to do share internet?
What would happen with bridging the two nics?

I am thinking something here on why it slows down so much.
My situation I have 2 nics, one is gigabyte, other is 100mb.

NOW, if you turn on ICS, in my configuration, it is like plugging a 100mb device into a gigabyte network, the whole network speed drops to the speed of the lower device which is at best 100mb speeds. It is in a way, bridging the network, adding in the lower speed nic onto the higher gigabyte lan.

If the other NIC was gigabyte plugged into gigabyte router, then maybe lan speed would stay high.

Any one think so?

What If I bought another gigabyte nic and used that plugged into a 100mb router, would that also drop the LAN speed?

If so, then I will just have to keep this gigabyte connection separate from other routers and nic cards. I am not wanting to buy new routers or switches or cards.

JFYI, I dual boot this PC with ubuntu. when I 'share the connection' (internet) to the gigabyte card, with low speed card connected to router to internet, my speeds run from 35 to 50 MB/sec when copying files from win7 to ubuntu PC on the gigabyte nics. versus 10 MB/sec using only win7 OS.