My domain is weaverfamily.com It's running Gallery 2 on drpepper.dreamhost.com. I find the speed to be acceptable during off-peak hours, but horrible during the day.
Looking at average port traffic is interesting, but not as relavant as burst speed. Here is a simple example. Time how long it takes to copy a 50 megabyte file over NFS. Assuming there is no other competing traffic on the link it should take about 5 seconds on a 100BT link, and about 1 second on a gig-e link. So if these servers are only connected at 100BT, it's going to take Gallery/Apache longer to fetch files from the NFS drive no matter how busy the link is, simply by the fact that it's a smaller size pipe, and it takes more time to transfer the bits through a smaller pipe.
We run gig-e everywhere not because our links were averaging more than 10MB/s, but because when we do a file copy or NFS write, we want it to go fast.
The argument you're making is basically saying that there is NO performance difference between 100BT ethernet and gig ethernet if the link isn't loaded, and that just isn't true, the gig link is 10X faster for every operation.
Since you said you have some hosts on gig, I would like to request my hosting be moved to one of these servers, because right now, it really is unusable.