Have now done the test with AVAST 5.0.332 free and wireless conection to linksys WRT610N
downloaded XP-SP3 316mb
Win7 - defender and firewall
have run ccleaner between each download
avast on
1: 14.39 369 kb/sek
2: 15.07 357 kb/sek
3: 15.20 352 kb/sek
avg: 14.88 359 kb/sek
avast off
1: 15.59 337 kb/sek
2: 13.26 402 kb/sek
3: 12.54 418 kb/sek
avg: 13.79 385 kb/sek
so my conclusion to this highly scientific test....
.... is that the slowdown is minimal
and that the web shield is fooling the speedometer at speedtest.net