Simple Windows Network Performance Question

I need help settling a debate.  My company has two floors.  A top floor & a bottom floor.  The software guys are all on the top floor using a gigabit switch.  The sales staff is on the bottom using a 100BaseT switch.  The router has a 10 megabit WAN connection.  

If one of our software people were to download a 2 GB file from Microsoft, for instance, using Internet Explorer w/ no 3rd party download accelerators, would that noticeably affect the network performance for the other employees?   My company will often have 1 or 2 remote desktop connections (or G2M) running simultaneously, but other than that, nothing out of the ordinary goes on during normal activity.  

Personally, I've downloaded simultaneous files that took a little time to complete & I've never heard a whisper from anyone, but it's turned into a dispute with someone .... and honestly, it's been over 10 years since I've had to do any network performance calculations.  I frankly don't remember how to justify my point.  

Can anyone help me with calculations to justify my opinion on this?   ...or if someone disagrees, throw me some calculations that would disprove it.  I know I've not been very detailed, but this doesn't need to be.  I'm just simply trying to put this to rest with him once and for all.  I work with older IT people that are accustomed to older ways and older understandings.  I'll be hard pressed to believe that a standard Windows download w/ no acceleration could have that kind of affect.

Thanks!