Yeah, Windows 7's speeds with single connections are very, very slow. It took me years to figure out the reason were bad TCP settings, because it worked fine when I used a multiconnection downloader. What fixed it for me was running these 3 commands in a CMD with admin permissions:
netsh interface tcp set heuristics disabled
netsh int tcp set global autotuninglevel=normal
netsh int tcp set global congestionprovider=ctcp