The problem with MT documentation is that it mostly documents state of art according to most recent ROS version at the moment of writing/updating (and documentation is not necessarily always up-to-date) and often doesn't mention version when certain feature got implemented.
In particular: RT switch chip in RB4011 had extremely poor support until around ROS 6.47. Which is what wiki documents. With ROS 7.1 it got decent support and that's what docs documents. Could be MT improved parts of support in recent 6.xx versions but not as exhaustively as in 7.1 (nah, that's probably not it do who knows where the info about RSTP with HW offload came from, possibly a copy-paste error). Funny thing is there's a remark about VLAN HW support starting with 7.1 but no such remark regarding MSTP which is inherently a VLAN stuff (in theory not so much but in practice for non-VLAN deployments MSTP is mostly not necessary, RSTP does the trick).
Now it really depends on particular ROS version @OP is running on his RB4011 ... Personaly I wouldn't go for 7.1 on any device used anything but as lab test unit. Which means the safest way of getting decent performance is to disable RSTP unless OP really really needs it due to network topology.