I cannot reach high load as I am still stuck at 1Gb/s because of the CCR2004 router not applying fasttrack.
The thread for the CCR2004 is in the beginner section as I did not want to migrate to this thread.
http://forum.mikrotik.com/t/ccr2004-1g-12s-2xs-slow-nat-performance-fixed/151468/1
I will test with iPerf3 on two VLANs and report.
The fan question is essential as I might ship back the CRS312 and buy a fanless Mikrotik switch with swOS.