Is that a MyBook Live?
A valid test is not a data backup process.
First of all what software are you using to backup? if you are using timemachine, make sure you connect via AFP://WDMyCloud.local.
Secondly, all backup software are intrinsically slow for the fact that you have varying sizes of files (All small files will slow down any copy speeds) and the fact that backup is suppose to be a non-invasive process (ie. works in the background).
So before we trace down why your backups are so slow… find out if you are really at gigabit speeds.
One of the nice thing about the Cloud device is that you can actually directly connect the device via ethernet to your mac ethernet. This bypasses the router to enable you to test. This is one way.
Or eliminate all devices from the router except your Mac and the WD Cloud device.
Find a file approximately 700MB in size. Writing to the Cloud device should give a result of about 15-20 seconds to copy this file over and to copy it back should be approximately 10 seconds ±5 seconds. This is the ball park timing for gigabit speeds.
If you are getting minutes, then you have to identify which part of the network is holding you back. You can try directly plugging the device from etherport to etherport which eliminates the router to see if that works…
If the router test is successful, plug in other devices to see if that slows down your network.
Remember one thing, the mac allows both the wifi and ethernet to be both on simultaneously. Make sure you turn off the WIFI, otherwise your testing may be skewed by the WIFI settings.
Getting Gigabit speeds on your network is independant of the backup speed as backup has it own speed problems including organization, fragmented writes and packaging; mainly due to the large number of small files that the backup process has to keep track of.