google tcp window scaling and disable it. worked for me. ( netsh int tcp set global autotuninglevel=disabled )
Win7 x64. went from 15MBytes/sec to 114MBytes/sec
The default values work fine for normal networks. The main feature is that it can scale itself larger for higher latency connections, but this is mostly good for sat links, so it doesn't help much on regular cable/dsl/Lan.