what version of windows are you using? I'm guessing windows 8 or 10 for the following
from your info above you just did a clean install... did you do it UEFI mode? if not it will be slower trust me I know i missed that part with installing windows that you had to go into your bios and select the usb driver there to install as UEFI
a video that shows easy way to check if you installed it in UEFI mode
https://www.youtube.com/watch?v=kyEqJ69Zv_s
and fyi i think your drives read and write speeds are ok. i have two Samsung ssd (830 and 850) and ive never seem to get the IOP that they claim they should do. i don't know why but i don't care as my pc boots in 5 sec.