I am transferring files between two wireless Windows laptops (each reporting 65Mbit), each connected to their own access points which are connected by a 100Mbit link and a network that is mostly (for what I can tell) devoid of traffic except for this transfer. However, the files are transferring at a total of 780KB/s (about 6MBit). Does anyone know why it is running so slowly?
Could you try the following:
If things are slow in step 1 then the problem is not in the wireless part. Maybe the connection between the two access points it bad. Maybe a laptop is slow in providing the data.
Steps 2 & 3 should allow you to eliminate a possible problem in the combination of one laptop and its access point.
If none of these shows anything, try transferring different data. (E.g. use a benchmark tool, or switch from CIFFs/Samba to FTP).
Check that the access points are in different channels. Ideally, you would want one on channel 1 and the other on 11 (or whichever are the farthest apart in your country). Also check the protocol that you are using. SMB (windows file sharing) is much slower than FTP for example.
 Also try archiving the files. It's more efficient to transfer one large file than may small ones.