Despite hard testing i was never able to get close to the thermal throttle limit, this is the biggest reason why it performed better than the sabrent rocket 4 plus, its unclear if sabrent rocket 4 plus would even be slower given enough cooling.
Unfortunatily the performance was still rather lame but what better option is there?
Costumer support was contacted
I contacted them regarding the disappointed sustained write speed and they didn't mention any way to improve that so the issue is probably just lack of a proper driver.
Samsung has not provided anything official for the 980 pro. I asked them how the following reviewer was able to use a proper driver and they just replied with "there is no NVME driver for the 980 pro" even though there clearly is one that you can get working with the drive for better results.
Some people are having SLC cache issues
I was worried maybe my drive was defective since other people were having issues but given the bad CPU i am using (r5 3600) there is probably nothing wrong with the drive itself in terms of hardware. The following individual however wasn't as lucky
Yep, I'm in the same boat then. Out of the box with zero data on it the drive benchmarked at about 5 GB/s in Samsung Magician. Last night I did a benchmark and it's about 1.2 GB/s. I was pretty shocked but learned that this is indeed a thing with these drives. Maybe a dedicated NVMe driver will solve it. Something with the SLC cache not clearing is causing the dip in speeds. I'm no expert, obviously. Read speeds are still blazing fast tho.
SLC-cache issue replicated
I was able to confirm that when the disk is mostly full it can take a very long time for the SLC-cache to rebuild. The sustained file copy speed seem to improve slightly which can due to the drive no longer being extra slow after recovering from SLC-cache exhaustion (bigger SLC-cache typically mean worse performance after it has been used up). Write was measured to be higher than samsung specified in crystal diskmark.
Despite testing the drive very hard (reading 80 GiB multiple times) performance didn't degrade at all.
Its unclear why the file copy speed in linux and windows is only half that speed.
The more serious issue is: why did random 4K Q1T1 drop to 50.48 ?