Samsung SSD EVO vs Samsung SSD PRO

About half a year ago Samsung released two pretty fast SSDs:
1) https://www.amazon.com/gp/product/B01LXS4TY6
Samsung 960 EVO
$479.99 for 1TB


2) https://www.amazon.com/dp/B01LYRCIPG
Samsung 960 PRO
$579.99 for 1TB


As you can see, PRO version is exactly $100 more expensive than EVO.

Does it worth?

According to specification:
960 EVO sequential read is up to 3.2GB/second.
960 PRO sequential read is up to 3.5GB/second.

However the reality is about 40% slower than advertising specification:
On my home server I got about 2GB/second sequential read for 960 EVO, and about 1.8 GB/second for 960 PRO.

To benchmark my SSDs I copied several files with ~80GB size into nul in Far Manager.

I used this motherboard (which is quite modern):
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https://www.amazon.com/gp/product/B01MR0H84F
ASUS Motherboard, (PRIME Q270M-C/CSM)

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Do you know what could be the reason why I cannot get promised 3.2 GB/second?
And why PRO has slower performance than cheaper EVO?

I even swapped PRO and EVO between NVMe slots on my motherboard, but the results were consistent: PRO was slower than EVO.

Update (thanks to mugunin):
Finally the benchmark that looks similar to what I measured (sequential read):
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http://www.storagereview.com/samsung_960_evo_m2_nvme_ssd_review
In our 2MB sequential benchmark, the Samsung 960 EVO recorded the best results in read with 2,308.5MB/s—even beating out the 960 Pro. On writes, it came in second with 1,660.9MB/s, only losing to the Pro version.
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