Opinion for my draft pc build

Solution
You can change the Samsung SSD to a similar spec M2 driver / card, then change the slow spinning HDD to a faster one. In the real world the spin speed of the HDD wont make a huge difference but if you ever use benchmarking tools to check transfer speeds you would see it
Unless I am missing something there doesn't appear to be a Motherboard in that list ?
I would suggest changing the HDD to one with 7200rpm spin speed - all the other components are aimed at the performance end of the market so why go for a slower HDD ?
M2 SSD's offer a slight performance boost over SSD's connected via SATA - I have both in my PC at the moment, in some cases you notice a slight improvement - but mostly there is little to choose between them
 
You can change the Samsung SSD to a similar spec M2 driver / card, then change the slow spinning HDD to a faster one. In the real world the spin speed of the HDD wont make a huge difference but if you ever use benchmarking tools to check transfer speeds you would see it
 
Solution