The answer is: it depends.
Are these users doing it over an 8 hour workday or do they upload this information in a one-hour period?
What are you willing to pay for internet access?
Where are the files being uploaded to? US, Europe, Asia? – more bandwidth does not necessarily help if the destination host is a long ways away
Are you doing any VPN on this traffic? VPN encryption will reduce performance due to the encryption overhead. It may not be real noticeable but it is there.
These file sizes and the number of users does not seem to be large. I would think that you could get by with a T1 (1.5 Mbps) or similar. A T1 will give you symmetric upload/download speeds. A DSL link is typically limited in the upload direction. You can get symmetric DSL (SDSL) but it may be an additional charge.