You need $10 to make a pihole DNS appliance to block ads. It's night and day, even if you have essentially unlimited internet access speed and minimal latency.
Even the $5 raspberry pi zero wireless module and a few GB microSD card will work fine.
As far as how accurate are speeds tests, well they're accurate for measuring the speeds of a speeds testing site, and little more than that. The effective difference in a 10Mb gig or even 10Gb internet connection is nothing when looking at the typical add infested website. The higher speeds help if you are really transferring large amounts of data at a steady pace. This is not what happens when you go to say cnn.com and about
90% of what tries to render in your browser is garbage ads or trackers over hundreds of small, slow requests.