We have a dedicated godaddy server and it seemed to grind to a halt when we had users downloading only 3MB every 2 seconds (this was over about 20 http requests).
I want to look into database locking etc. to see if that is a problem - but first I'm curious as to what a dedicated server ought to be able to serve.
A lot depends on what the 3MB is. Serving up 1.5MBps of static data is way, way, way, within the bounds of even the weakest server.
Perhaps godaddy does bandwidt throtling? 60MB downloads every 2 seconds might fire some sort of bandwidt protection (either to protect their service or you from being overcharged, or both).
to help diagnose the problem, host a large file and download it. That will give you the transfer that the server and your web server can cope with. If the transfer rate is poor, then you know its the network, server or webserver. If its acceptable or good, then you know its the means you have of generating those 3MB files.
check, measure and calculate!
PS. download the file over a fast link, you don't want the bottleneck to be your 64kbps modem :)
Check netspeed.stanford.edu from the dedicated server and see what your inbound and outbound traffic is like.
Also make sure your ISP is not limiting you at 10MBps (godaddy by default limits to 10Mbps and will set it at 100Mbps on request)