Personally I'd fit a 3dB forward path filter to the back of my modem to bring the received power down. The SNR would fall too although, IMO, you can't get an SNR that's too high provided that the receive power isn't too high.
Those are the same figures, by the way, that you had when the outside wall was a mess.
Others have advised not to test your speed on Rapidshare but rather on the VM download site
http://www.virginmedia.com/testmyspeed/manual.php. Please do this and report.