Drastically slow G tech XL speeds vs G tech SSD

Hi folks,

Im running a G tech XL 70TB raid 5 on a 2016 Mac Pro and a 4 bay SSD shuttle drive with 2 x 4TB SSDs and 2 x red mini mag readers. I usually get 350-450MB/s but for some reason the XL gets 70mb/s while the SSD gets 400+. The system has been working fine for a good 8 months now (Im on a TV show and download 3-6 TB/day).

I keep a buffer of 20% free space on the XL at all times and the G tech utility software shows no signs of wear or a degraded drive. Any help would be welcomed.
Thanks