@Anakin1000 : Speedtest via a browser is pretty unreliable IMHO, I wouldn't read too much into the values, for what it is worth:
Speedtest App : 545 Mbps
Safari : Speedtest.net 483.79 Mbps
Safari : Fast.com 570 Mbps
Safari: Project Stream 344.799 Mbps
Chrome: Speedtest.net 407.54 Mbps
Chrome: Fast.com 560 Mbps
Chrome: Project Stream 504.316 Mbps
Firefox: Speedtest.net 545.81 Mbps
Firefox: Fast.com 610 Mbps
Firefox: Project Stream 529.488 Mbps
As you can see a lot of different values from different browsers and speedtest tools.
From time to time (maybe 3 times a year) for reasons still unknown to me my MBP WiFi speeds drop significantly, a restart resolves the issue for me, but I don't have the patience to try and investigate what the precise cause might be, life being too short than try to figure that one out.