My two cents.
File size has EVERYTHING to do with the number of concurrent connections (sessions) a server can handle.
From a connection standpoint, your server MAY get overloaded serving such a large file so many times in one hour. You are not factoring the speed in which the (a) connection closes and opens.
On a properly tuned OS running the right http software, you could see something like this. (Sessions /sec vs content size)
Your hard limit of 100 Connections a second sounds like either a File Descriptor limit (that can be changed depending on the OS), Memory (or in this case memory buffers size).
First, I would find out if you can set your max concurrent sessions higher in the OS. This is also known as File Descriptors. It?s the control in the IP stack that accounts for each session, and disallows any others if the hard limit is reached. This is a tunable parameter in the OS.
As for memory buffers, this depends on how much memory you system has. This is the memory table that keeps track of connection state, etc. Too much to get into here. Anyway? you can crank this up.. but it could cause an issue with machines with a small amount of memory. To uncomplicate it, the larger the memory buffer, the more connections your system can keep track of vis-a-vis serve.
There are a few other OS parameters to tune to make this work, too many to list. Look for white papers from your OS source (you can always find Performance Optimizing XXX OS) somewhere. Deja.com is also a good place to look.
Check your speed and duplex of the NIC. 100 or 10 Mbits / Full or Half. Most likely you will have 100 Full. Check anyway. Anything other than 100 Full your config will cause latency and packet loss.