If gpu off gives you better results then yes probably it is not the drive.
Mostly people get drop on drive issue. You could run some drive tests.
You will never know maybe one of the drives is bad or is going to be bad etc.
Just run BM drive test and you will see what it sees.
Id take all possible cases and eliminate them one by one.
Just be creative and methodical. Always consider problems in co operation.
I had to turn off gpu support in motion for instance. Now all is smooth as silk.
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Margus
https://iconstudios.eu