Only send connections to server2 if connection limit reached on server1

I have 4 HTTP web caching servers in a pool, and we want to try and increase the cache hit rate (likihood that it will have already cached the requested page) by focusing all connctions on one server until it reaches a high number of connections, and needs new connections to be shared to other servers in the pool instead.

E.g. I want to send all connections to server1 only, until server 1 reaches a connection limit I have set (say 500, TBC). Then only during the time that server 1 is at its configured limit, i want it to then start sending new connections to server2. Server 2 will have a limit set as well, say 500 again, and if we get to a point where server1 and 2 have both reached thier limit, it will start sending to server 3, then server 4 if needed. Perhaps server 4 could have no limit set, so that the pool overall status does not reach its limit, as it would be better to respond slowly if needed than stop responding completely.

Could this be done with a combination of Priority Activation groups and Connection Limits? E.g. Priority Group Activation = Less than 1. * Server1 = Connection limit 500 + priority group 4 * Server2 = Connection limit 500 + priority group 3 * Server3 = Connection limit 500 + priority group 2 * Server4 = Connection limit 0 + priority group 1 If so great, but if there is a better way to do it with an irule perhaps, let me know.

Thanks in advance.