While most of the users who went to the 1gbps service opt for the RT-AC68U, I selected the lesser RT-AC56U instead. With the latest firmware, I ran into the same infamous issue of low throughput speed. For my case it was "capped" at 300~314mbps.
After speaking to MR live chat.. surprisingly was rather fast unlike what some other users encountered. Solomon came into the chat and assist with the testing and we concluded that it could be the ASUS firmware causing this "cap". While upgrading the latest and best firmware is the usual practices, I decided to paddle backwards and try from the older firmware and I did find one which did not face this issue.
For the RT-AC56U, the version unaffected is
3.0.0.4.374_583. For those using this router you might try out this firmware if yours isn't already shipped with one. It is noted that the elder RT-AC68U shares the same code base and there is the same version of the firmware available for download and if anyone is free, do give it a try and see if the low throughput issue resolve a not.
Results from
http://speedtest.myrepublic.com.sg/
Run 1:
Download Speed: 851330 kbps (106416.3 KB/sec transfer rate)
Upload Speed: 475266 kbps (59408.3 KB/sec transfer rate)
Latency: 2 ms
Jitter: 1 ms
5/6/2014 11:52:03 PM
Run 2:
Download Speed: 798323 kbps (99790.4 KB/sec transfer rate)
Upload Speed: 477649 kbps (59706.1 KB/sec transfer rate)
Latency: 2 ms
Jitter: 1 ms
5/6/2014 11:53:16 PM
Run 3:
Download Speed: 815980 kbps (101997.5 KB/sec transfer rate)
Upload Speed: 475783 kbps (59472.9 KB/sec transfer rate)
Latency: 3 ms
Jitter: 1 ms
5/6/2014 11:54:10 PM
Speedtest.net results from an earlier run on direct ONT