I would suggest using connection limit at the node level for each server so that when server reaches to a limit it stops accepting connection while serving the existence connection.
When all servers reaches to the limit then LTM start dropping all the new connections. In order to avoid this situation you can use the active_member command in iRules to detect this condition and redirect all your request to a virtual waiting room.
Virtual waiting room is nothing but running few servers with a static html page embedded with a html code that redirect your request back to the original servers after x number of mins.
let me know if its make sense.
Nimbostratus