Its kept @ 250Mb/sec by a built in policer (interface is normal 1 Gig offcource).
According to Meraki SE, this is implemented because they want to make sure, that the device in question will always perform the guaranteed 250Mb throughput, no matter what type of inspection etc. you throw at it... also they have to keep cpu "overhead" for some of the upcoming features..
So yeah... if you try to do a test with iperf etc... you will se, that it is more than capable of doing +300Mbs, but then the policer kicks in.
I would have liked the opportunity to use it at its full capability, but i respect the choice Meraki made instead, guaranteeing performance up to a certain speed... you know what you get.. no tuning or shortcuts needed 🙂
Best Regards
Ole