This seems like the best place for this. I will mention specific files/software/cameras, but this really isn't unique to any of these, but more a general question/discussion.

I have a file server (Netgear ReadyNAS) that hosts all our video files for several editors. We can normally get around 80-100 MB/Sec read speeds which (up till now) have been fine since usually not all 3 computers are reading at the same time.

We shoot mainly on EX1Rs and 7Ds. When editing one or two clips at a time, we have had no problem. But now we are trying to multicam edit (Premiere CS5 w/ Mercury) 4 cameras/clips and it seems to be clogged down to uselessness. This was tested with no one else connected to the network.

What's weird, though, is I can embed about HD 6 picture in picture clips onto the same project and the network seems to be able to support the bandwidth just fine. I add the 7th clip and it chokes out.

Why do you suppose we can't do multicam editing with as much ease?

It's a gigabit network with 80-100 MB/Sec read speeds, and 50-80 MB/Sec write speeds.

Multicam is probably trying to stream, where normal editing would normally only stream a max of two at a time all files simultaneously - the bottle neck could actually be CPU/GPU if you are editing natively and those are compressed format. Have you tried streaming different, less compressed codecs with similiar/higher bitrates to check?