You can get a good link with high end networking gear with extremely directional antennas. However, the best you can expect reliably is around 100Mbps physical throughput, with a good quality line of sight connection, on a 5Ghz wide channel link.
For transferring 10 MB files, it shouldn’t take longer than 1-2 seconds. 100MB+ files will really start to trash the thing, especially if you have a few users doing this at the same time.
Wires work very well, and would be a vastly superior option, if you can make it happen.
Ya Cisco has quite a lineup of point to point and point to multipoint setups but they usually get 54-104Mbps on a good day.
You probably have firewall at your main location and if its above a Best Buy Linksys “firewall” then you can easily built a VPN tunnel on it. Have the new location install broadband and put their modem in bridge mode. Buy a Netgate, Juniper SSG, or Fortinet firewall for less than $800 and built a VPN tunnel. Simple, cheap, and will get you the best speeds.
Here is a Juniper SSG 5 that does what you would need for $150
If you get the model of what you have at the main location, you can easily do this.
Setting up a static point to point VPN would be easy enough and take care of any kind of traffic that you might encounter. But another thing we use here at the college are the Ethernet to DSL convertors, might only have a 40-60 Mb connection but if you only have 10 users and they aren’t on Facebook all day that would be sufficient. (If there is available copper in the other building) But if you can afford it, pull fiber, you’ll never regret it.