thanks for reply Jorge, you centered the problem!
For this moment the machine has been moved for maintenance in other room, and not near the switch (probably problem with the cable? need investigation), I put it away, in orgin position and the write speed increase 10/15 mbs. The performance with or without cache are almost similar, something more without cache but not significant (3/5 mbs).
In attach the test with iperf3 from my client pc (in the second i changed the position of machine).
Then I did a test for write/read inside unraid from/to two shared folder (1 with cache and 1 one not) the speed in write are 140 mbs (no cache) 160mbs (cache).
after this result, the problem is not of unraid but of the network, probably my laptop connected via nic, the next steps are testing the netwoks with my client near the switch, and it's possible to change the network conf of unraid with two nic in bonding.
another note: instead I have not noticed variations using the nic realtek or intel.
thanks
Teo
test_iperf.txt
test_2_iperf.txt