those numbers seem quite low. are you using the intel NVMe drivers? the windows drivers handicap the performance.I have one of these in my workstation...not bad. Here is my initial benchmarking results. The only thing that worries me about these is write endurance.
Test System:
Asrock X99M Killer
Intel 5820k
32GB Corsair LPX 4 x 8GB DDR4 2400
Zotac GTX 980TI
Samsung 850 PRO 256GB - OS - Windows 10 Pro
Intel 750 AIC 800GB
maybe sample size limited throughput? 1GiB vs your 4GiB?