For those of us who manage networks with Cisco 6500 series switches in their core, I am sure the wide array of high bandwidth switches from Cisco and their competitors have caught your attention. The 6500 series provides 10GB performance at 80Gig per slot when coupled with supervisor 2T modules. The question you should be asking ,is how much throughput do I need in the future?. If your bandwidth needs are growing exponentially and you want to have data center traffic traverse your core switches then upgrading your 6500 switch might not be a such a good idea since data center and its aggregated bandwidth demands can be significant in a medium to large organization.
However the drawback to acquiring new switches relate to their price, a Supervisor Upgrade would be much cheaper than acquiring a similar sized switch. Size though also does not truly reflect the state of affairs since they are now 2U sized switches that are able to out perform an upgraded 6509, example of such a devices can be found in the Nexus 5000 series switching line. If you run separate data center and user networks (as you should) then a 6509 with a supervisor 2T module results in a relatively inexpensive upgrade that will cause only minor disruptions and results in less headache at 3x your current performance. Upgrading your switch using a smaller unit will always pose challenges as it relate to re-cabling and re-arrangement of your core network which is always daunting due to the differences in the number of switch ports. Sometimes we need to stay put until we have a clear need for change, so if you are not oversubscribing your current infrastructure but want to future proof it then the supervisor 2T provides reasonable investment protection.