I use HP Meshing to create a loop between 5 4000m switches. My personal preference in this situation would be to put 2 * Fibre SX Cards(J4113A) into each switch, set these ports up in a mesh and link one switch to another in a loop. Not the cheapest way but it will give you a Gb backbone and I`ve found HP Meshing to be less troublesome than STP.
Cheers,
Russky