My understanding of the HTG article, is that the SSD slows down when the drive fills up because there are less vacant blocks to write to. And since there are less vacant blocks to write to, the SSD actually has to read the block into cache, replace the value and then write it back. This becomes problematic, especially for files greater than the block size of 256KB because the SSD is constantly doing this read-to-cache, replace-the-data, write-it-back dance. All this reading and writing slows the system down.
In your case, your SSD is less than 75% full but the C: partition is 81% full yet I don't see why that would slow the system down since the sum of data is less than 15% of the total capacity of the SSD. In other words, I don't know if there's a correlation between your poor performance and the 81% full C: partition.
But here's how you can know for sure:
Visit the manufacturers website to see if there are any firmware updates or SSD optimizers for download.
I don't know your SSD manufacturer but here are links to the top three:
Also you might want to check out the free SSD optimizer tool from Elpamsoft:
If you want hard numbers, quantitative data, that proves your drive is slow look at IOMeter. It was originally designed by Intel until it was discontinued and released under the Open Software License. You can find it on Sourceforge.
Finally, the SSDReview has a super detailed, eight page report, on optimizing SSD performance. If you're really serious about boosting performance dig through that article and you'll have everything you need.
I read through the article and synthesized 10 points that are relevant to your issue:
- Make sure your disk is in AHCI mode, not IDE
- Make sure all drivers are up to date
- Set PC Power to High
- Enabled Optimize Drives
- Enable Faster Boot through MSConfig
- Disable Multi-Boot Selection
- Disable Write Cache Buffer Flushing
- Confirm TRIM is actually working
- Adjust CPU States
- Get an SSD Toolbox
Hope this helps.