let me preface by saying I am no storage expert. I dable a bit but
you have 8 x 6 disk raid 5
so you have 8 x 1 raid5 parity disks (roughly), you can loose only 1 disk from each array before you are close to trouble ...
why not move to
1 big raid 6 ( with 1 or 2 hot spares).
leave you with 2 parity disks and 6 spare disks (2 of which you can assign to hot spare).
This way you have 48 - 2 -2 ( total spindles - 2 for raid -2 for hot spare ) = 44
44 spindles to handle all the io for all the sql servers.
where as you had
6 - 1 ( 6 disks in lun - 1 for parity) 5 spindles for each sql server.
BUT you might just have too much io for the setupp you have 
im not sure
there is more risk, if you loose 3 drives within the recovery period your hosed... on all the sql servers.
