No one covered one extremely important aspect: PS4 is very sensitive with cable length.
It was really frustrating to see my PS4 getting always under 100Mbps for internet speed test (usually 70-95 Mbps) despite I have a bandwidth of 500Mb and a 1Gb router.
The speed was always OK on my PC , but not on PS4.
Everything changed when I used a shorter LAN cable and now I get 400-500MBps. This definitely is not happening on PCs, is just about the PS4 network card which is sensitive.
My initial LAN cable had about 7-8m (which is short enough for networking) and the second one is ~3m long and is the cable which finally provides normal speed.
I discovered this when I moved data from one PS4 to a PS4 PRO, and the PS4 PRO was connected with a shorter LAN cable. Initially I thought that the PS4 PRO has a "true" 1Gb port, but that wasn't the case, as the cable length proved to be the real issue. I was also shortening the the first cable, to see if the speed decreases and it did, I was getting ~115MB/s with a ~5,5 m long cable so I did by best to have the shortest cable connected. Works just fine both on PS4 and PS4 PRO.
Nothing usefully found on the internet, just DNS stories, which can improve a bit the speed.
Hopefully my findings will help many of you.
At least my son is very satisfied after he downloaded a game of 25GB in about 10 minutes (~40MB/s).