Grounding PCB Within Aluminum Enclosure
Using method #1 as a basis, the wire is supposed to go to to a large pour that is NOT the ground plane on the PCB, but is split from it yet still connects at one point. All other things that might be hit by transient events must also connect to this plane (like connector backshells and cable shields).

The purpose of this is to provide a path for transient currents to flow to to ground while keeping the PCB at the same potential as the transient, yet not allowing the transient to flow through the PCB on its way to earth.

This automatically rules out #2 because having multiple connections to ground means that the transient current might flow THROUGH the PCB on its way to earth. Even if the earth plane is separated from the ground planes, the fact that they overlap introduces capactive coupling between the planes.

Connecting to just one point on the PCB with no split plane has a similar issue in that current spreads out when on the ground plane and this can flow under components which is why you want the split and connection to the ground plane at only one point.

If you can find a copy of Henry Ott's book it covers this in more detail in Chapter 15.

Here is a table that compares the impedance of soldered vs screw connections. It's not directly applicable to your scenario, but I think it indicates the copper screw and riser  method should be fine, as long as it's only connected to one point on the PCB. Since it's only a single-point connection, can connect straight to the ground plane in this case too since transient currents in the enclosure shouldn't be flowing through the riser. You don't need a mini-earth plane on the PCB (that is the conductive enclosure itself).

This connection point to the enclosure should be as close as possible to all cable shield connections to the enclosure, if you have any.



Taken from Electromagnetic Compatibility, Henry Ott 2009