CrystalDiskMark is a synthetic benchmark that tests both sequential and random small and mid-sized file transfers using incompressible data. It provides a quick look at best and worst case scenarios with regard to SSD performance, best case being larger sequential transfers and worse case being small, random transfers.
The Samsung SSD 850 PRO drives were incrementally faster than the majority of drives we tested in most of CrystalDiskMark's individual tests (especially with reads), save for the 512K transfer benchmark. In the all important 4K transfer test, however, the new Samsung drives simply blew everything else out of the water.
These are the kind of numbers CrystalDiskMark reports with RAPID mode enabled. As you can see, reads go through the roof, though write performance is boosted significantly as well.