Some models of the 960 series PCIe SSDs are already considered to be the fastest NVMe flash memory currently available. Now the 970 models are on the shelves and actually add another one.
Models of the PRO series are equipped with 2 bit MLC flash, the cheaper EVOs come with TLC (three bits per cell) memory modules. The 970 EVO series is available with 250 GByte to 2 TByte, the 970 PRO is "only" available with 512 GByte or 1 TByte storage capacity.
Compared to its predecessors, Heise has improved writing performance by up to 50 percent. Both models write around 3 GB/s for a short time. But even the cheaper 970 EVO does not fall below 2.4 GB/s even after a long writing time.
For PCIe SSDs we primarily see an application 
as render cache. And in this respect, the Heise test of the 970-EVO series hardly certifies worse suitability than the 970 PRO. However, the PRO version currently costs "only" 25 percent more than the standard EVO.
All in all, the flash market is currently going through a phase of relaxation. For example, 1TB-SATA brand drives can currently be found for less than 200 Euros. These are recommended as universal system drives. PCIe SSDs are almost always overqualified in this application scenario and the surcharge compared to SATA SSDs hardly pays off.
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