I've wondered about this for quite a while. Why does Meraki only offer up to 3m TwinAx. Are the SFP+ ports lacking sufficient power to drive a 5m cable reliably? Do they have some kind of timing issue?
I've changed my designs to only use the Meraki 3m cables to be safe (it would be expensive for me to get this wrong for a customer and have to pay to swap out for fibre).
If you try it out, let us know how it goes.