Does Mikrotik disable the tcp_slow_start_after_idle and enable bigger TCP_INIT_CWND in its kernel for better TCP performance?
net.ipv4.tcp_slow_start_after_idle=0
TCP_INIT_CWND 10
references:
http://chimera.labs.oreilly.com/books/1230000000545/ch02.html#_tuning_application_behavior