Mark,
     I guess "colocat or not colocate" depends on a few things
1) will the client fill an entire tape? if not you'll be wasting tape
space.
2) how many tapes will the client use
3) how much data is on each client. I have seen a full restore for one
client call for mounts of more than 80 tapes without colocation. It was
restoring 5 gb of data.
4) do you have multi levels of storage pools so that each backup client
doesn't wait for a tape mount when backing up if you are going directly
to tape........