I had been connecting my Sonnet 10GbE SFP+ adapter and my Synology NAS directly with a SFP+ 10Gbit copper cable. Per manufacturer instructions I set MTU on both devices to 9000 and experienced a significant performance increase in large file transfers. I could read from the 12 drive NAS at over 1gigaBYTE per second. I got the Mikrotik https://mikrotik.com/product/crs305_1g_4s_in which is just awesome, but my speeds are now slower - around 2/3 the speed or less. Is there anything else I need to do to unlock the power of this connection? I tried to go into the Mikrotik settings for the 2 ports being used and change them to 9000 MTU but the setting doesn't stick. Thoughts?

If you use RouterOS, the ports are members of a bridge - what is the bridge MTU?