It would be a good idea to connect your PS4 via Ethernet and check the throughput. In my home I can see throughput degradation ranging from 10% - 50% depending on where I make the connection. Sitting next to my cable modem/router I can achieve 90% - 100% of throughput (compared to a wired connection). A wall, a floor, and/or other wireless devices such as telephones can cause serious degradation of the signal - and throughput. You might also want to use a wired connection to baseline test your PC and/or laptop so as to eliminate any PS4 issue.
Using the process of elimination it becomes easier to identify where the problem lies. If you eliminate potential problems on your side of the ISPs modem it is always easier to receive support as opposed to excuses.
Speedtest.net uses the OOKLA flash-based Internet speed test. OOKLA has a unique way of measuring speed. First, they drop the bottom 10% and top 10% of throughput measurement as they perceive those to be outliers. Then they drop another 20% of the bottom as they consider it represents a ramp-up. Effectively, they are reporting back on 60% of the time the test is run. Also, the Flash-based tests are relatively short duration. When I run a large file test here (testmy.net) I see a ramp up, a surge will above the speed I pay for, and then a fairly consistent throughout at the expected throughput, followed of course by a ramp-down. Running a small-file test (akin to the size test Speedtest.net utilizes) I can get exaggerated throughput results - much like I can see from Speedtest.net.
If a Internet user is consistently uploading/downloading short bursts then the Speedtest.net would seem correct or accurate. On the other hand if you are streaming video it is more accurate to look for the throughput that is sustained - as you might see when doing a large file test on testmy.net.