BACK UP NOW!
The hard data that supports Dominic23's conclusion is here:
Performance:
System Load: 1.30 (1 min ago) 1.31 (5 min ago) 1.58 (15 min ago)
Nominal I/O speed: 7.21 MB/s
File system: 124.00 seconds (timed out)
Write speed: 4 MB/s
Read speed: 200 MB/s
Both values should be roughly 250MB/sec for your computer and that model drive. With a write speed of 4MB/sec, I am surprised the computer worked at all.
Based on many reports here, the SSDs the work best in Macs are Crucial's MX series and those from Other World Computing. Too many on the obscure brands are of low quality and/or were never optimized for Macs.
Also, the Hitachi drive is much slower than the computer can handle. Both the main drive bay bus and the optical bay bus are rated at SATA 3GB/sec; your Hitachi is only rated at SATA 1.5GB/sec.
I would remove Drive Genius. Such tools were invaluable in the early days of macOSX but the OS is so evolved now that our old, "must-have" third-party tools are not needed, and can actual compete with newer features built into OSX.
Yes, replace the drive cable when you replace the SSD. I get drive cables here:
https://eshop.macsales.com/item/Apple/9229751/