ReadyNAS Ultra 2 LAN slow

Thanks StephenB!

So this is what I did today:

I have used two different LAN Cat 7 cables to make sure those were not the problem.
I have disable all other comunication cards on the PC (wifi/Bluetooth/ unused LAN).
Jumbo disable.
MTU onthe NAS set on 1500 then to 1472 with no changes in performances.

First attempt.
I have connectet NAS LAN Port 1 with Realtek PCIe GBE Family Controller of the PC.
Configuration:
NAS
IP 192.168.168.1
Subnet mask: 255.255.255.0
Gateway 192.168.168.2 (the PC address)
PC
IP 192.168.168.2
Subnet mask: 255.255.255.0
Gateway 192.168.168.1 (The NAS address)
Result:
Moving a 4 GB file with drag and drop: 90 MB/s for 3s", then drop to 0 MB/s, then raise to 20 MB/s for 2"s, then drop to zero...then stuck at 512 kb/s..

Second attempt:
I have connectet NAS LAN Port 2 with Intel(R) 82579V Gigabit Network Controller of the PC.
Configuration:
NAS
IP 192.168.168.100
Subnet mask: 255.255.255.0
Gateway 192.168.168.50 (the PC address)
PC
IP 192.168.168.50
Subnet mask: 255.255.255.0
Gateway 192.168.168.100 (The NAS address)
Result:
As before. Start at 83 MB/s, drop to 0 then raise and drop, with the highest peek at 2.78 Mb/s, lowest 0. Ii seems to be stuck most all the rime

Last attempt:
I have connectet a Surface Pro with a Giga LAN adapter to the NAS Port 2.
I gave the Surface the same configuration that the PC had.
Result:
Start at 83 MB/s then drop to 0...

So I am sure the problem is not the PC or the cable.
Please tell me if there is any other config attempt I should try.
I have already done 2 factory reset and I have overwrite the firmware once.

One sidebar question: as I have formatted and reinstalled everything in a Raid 1 configuration, now it showing me that 1% of the free space ( 47 GB) is already taken (not by me). Is that normal?

Thank you in advance!