Slow iMac read/write speed, help appreciated

Hi,

I have noticed some surprisingly low performance readings when using the Blackmagicdesign's Disk Speed Test on my late 2013 27inch iMac. The top readings I've had are a write speed of 160MB/s & a read speed of 170.1 MB/s.

I use the machine for work to host a DAW & for checking e-mails/stream video, but soon my work will involve some video editing so these readings are concerning. Aside from clearing cache, running first aid in disk utility & recovering from TimeMachine which I've tried, is there any other solution I should try to increase performance? Or does such a low reading suggest there's something seriously wrong?

I've previously contacted an Apple representative about this via chat & was advised to bring it in to my nearest store, but I need it on a daily basis for work so am reluctant.

When I bought the iMac in early 2014 I went for the highest spec you could go for & I still have over 200gb of free space on my 1 TB SATA disk/Macintosh HD

OS X El Capitan (10.11.6)

3.5 GHz Intel Core i7

32 GB 1600 MHz DDR3

NVIDIA GeForce GTX 775M 2048 MB

Thanks