Larger ssd devices are a bit faster.
Buy a single 500gb ssd. It will be easier to manage space on it and it will be faster. Not by much, but faster.
The Samsung 950 pro will have impressive synthetic benchmark speeds, but it really makes little difference in normal operations.
I Know, I changed a Samsung 500gb 850 pro for a 950 pro and noticed very little difference.
Virus scans are faster, but that is about it.
Samsung evo is good.
If you need to store large files such as videos, that is where a hard drive is good.