I have a Catalyst 4507R running as the core in my network. This switch doesn't do anything special, as all routing is handled by the 6509 that this switch connects to(network under a network basically) I want to upgrade my switch to the 12.4 IOS and will have downtime this week to do so. I've never been good at figuring out which IOS to install, any ideas on which one to choose? I'm running the Supervisor II Plus engine with one GB Fiber uplink card, and two copper uplink cards, one running GB, the other 100MB. Please advise.