PCI-Express SSDs are still quite expensive, but they also perform significantly better than SATA600 SSDs. A few years ago the additional price you paid for a high-end SSD barely gave you better performance due to the SATA600-bottleneck, but now the difference in potential is very big. However, these differences are seen with models that are quite a bit more expensive than the SATA600 models. If you are not prepared to pay the required premium, we recommend you to stick with the SATA-models for now.
Samsung remains the dominant player in the market of PCI-Express SSDs. With the latest 960 Pro the manufacturer even outperforms the Intel 750 SSD, which held on to the performance crown for a long time. The 960 Pro does not only perform excellent in benchmarks that simulate professional use, but is also the fastest in the real-world PCMark 7 and 8 tests - although how much of this you can actually perceive is up for discussion. The SSD is not inexpensive, while the price per gigabyte for a PCI-Express SSD is not extremely high. As the best and fastest SSD it receives an Ultimate Product award.
While the 960 Pro covers the top segment, the 960 Evo drives perform excellent in the PCI-Express mid segment. Despite their low price per gigabyte, they still perform extremely well - even better than the 950 Pro. At the same time their PCMark performance is slightly worse and the write speed of the models with lower capacity is, outside of the buffer, somewhat slow. Nevertheless the price-performance ratio is extremely good, especially with the 500GB and 1TB models that we tested. Therefore these receive our Excellent Choice award. We can definitely imagine that the relatively limited price difference with SATA-SSDs does not withhold you from picking up the slight boost in performance.
Lastly an honourable mention for the Intel 600p. While it is barely faster than the fastest SATA600 SSD, considering its low price it can be an interesting alternative for certain desktops or laptops - but only if the M.2 slot in question supports the PCI-Express standard, which is not always the case.