For me there isn't any real difference even with the web shield enabled. The major difference is my broadband package is up to 38Mbps download and 2Mbps upload. This is Fibre Optic cable to the cabinet and normal copper cable to the house (about 200 yards).
My average when tested usually works out at 37Mbps down and 1.7Mbps up.
Some considerable time ago avast mentioned that there should be no appreciable difference up to 100Mbps after that the scanning will be the bottle neck. I don't know were avast stands right now regarding that previous statement.
So your on very fast connection, so the above may be what is happening. You could try this and see if it makes a difference - avastUI > Settings > Active Protection > Web Shield > Customise > Main Settings - and uncheck the 'Use Intelligent stream scanning.'
That may make a difference for your browsing, but I don't see it making a difference in speedtest.net check as the file size is relatively small - a possibly better test is as Pondus mentioned download and test a large file - with and without the Use Intelligent stream scanning enabled.
EDIT: test run with Use Intelligent stream scanning disabled, not a huge difference, but closer to mu theoretical maximums.