What type of drives do your laptops have? Remember, file transfer is not just limited by your network connection, but also your drive speeds. There may also be an issue with how fast the OS can transfer the data as well, especially if it's processing other data or apps in the background.
Interestingly enough, the throughput you're getting (~35MB/sec) is about right for a USB 2.0 connection. So, perhaps with a little more info on the laptops' specifications, we might be able to better pinpoint where the problem is at.