Internet troubleshooting - (this thing is slow at night)

[tr0910]

I'm fed up with slow internet in the evening.  I need to figure what is wrong and hope some of the networking experts can point me in the right direction.  The connection is fiber 200/20 and at 8am in the morning, I get speedtest results of 307/36 with a 2ms ping.  This is awesome, but by 8pm, the internet gets glacial.  You see it especially bad when just normal web browsing.  Now the connection seems to be able to download fast even in the evening.  I can torrent down a Linux distro without noticing the lack of speed in the evening.  But, normal browsing is painful in the evening. 

 

Rsync over SSH really shows the problem big time.  If you graph download speeds of rsync over SSH you will get 5 megabyte/sec sustained transfer rates for zip files over 100mb in the morning.  But by evening the rsync speed will drop to sustained rates of less than 56 kilobytes/sec.  (this is rsync from China to a server in USA)

 

How can I narrow down what the real problem is? 

 

(I am behind CGNAT on China Telecom, and since the provided modem/router is limited, I have my own router, a Netgear 6300 running DD-WRT.  So I am double NATTED.  I have tried Google DNS, but presently I have my router set to 0.0.0.0 so I use the default DNS provided by China Telecom)