I've been trying to figure out why after a few restarts my Intel 750 read speeds drop drastically. I've reinstalled Windows 10 6 times on this drive. Speeds are amazing before installing any drivers/programs. Than the drive stays at the middle speed for a few than all of a sudden it gets slower. Nothing is running, disk usage is at 0%. The Intel NVMe driver is installed and I ran the Intel toolbox optimization multiple times. Trim is enabled and working.
Speeds before drivers
After installing drivers. Speeds are still fine
After a few days of use
The performance of an SSD is at its best when the SSD is new (out-of-the-box). As the SSD fills with data, performance will degrade. Performance degradation varies based on the workload applied to the drive. Benchmark tests are expected to drop as the drive usage increases.
You can make sure you SSD is working correctly by using the https://downloadcenter.intel.com/download/23929/Intel-Solid-State-Drive-Data-Center-Family-for-PCIe-... Intel® Solid-State Drive Data Center Family for PCIe Drivers, also, make sure TRIM is enabled or run the SSD optimizer with the most recent version of https://downloadcenter.intel.com/download/18455/Intel-Solid-State-Drive-Toolbox Intel® SSD Toolbox.
The http://download.intel.com/support/ssdc/hpssd/ssd-750/sb/intel_ssd_750_series_evaluation_guide_332075... Intel® Solid-State Drive 750 Series Evaluation Guide has details about how the SSD performance is measured, it mentions the tools, hardware, configuration and procedures used. The advertised performance from the http://www.intel.com/content/dam/www/public/us/en/documents/product-specifications/ssd-750-spec.pdf Product Specifications (Page 8) is obtained using http://www.iometer.org/ Iometer* with specific test parameters. The results you provided are from tools that use preset parameters, so the results will be different (higher or lower) from the advertised in most cases.