OP, I had so much troubles with PSN. People will tell you anything, that it's your fault, your ISP fault or your country fault, but never Sony fault.
While I don't blame Sony directly, I blame their CDN set up which is very picky and unreliable when it comes to routes. For some reason it just not able to select fastest CDN server based on your location, that's why screwing around with DNS might improve your speeds.
My speeds went from 5-10Mbps to 20-50Mbps when I changed to Google DNS. Mind you, I am on 1Gbps fiber and Xbox can handle 150-300Mbps... Through Wi-Fi.
You can read about my woes with god damn thing
in this thread. It is the reason why I buy digitally on Xbox, and only physical media on PS4 (with few exceptions).
If you cbf read the post, here is quick video to summarize the difference between XBL and PSN, when it comes to speeds:
http://www.neogaf.com/forum/showthread.php?t=827626
Although, thread and video are a bit old, I was able to set up DNSMasq and through trial and error find CDN server which had best speed for me, with 20-50Mbps speeds, sometimes up to 80-90Mbps, but it's still a far cry from XBL.