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Yes, there's a potential performance issue with stacking. Remember stacking is a daisy chain, so with more switches, there's the potential to push more transit traffic between stack members. Larger stacks may also introduce additional latency.
If this isn't clear, visualize a similar situation with nine switches that don't have stack technology. You might connect all nine in a serial daisy chain, or you might have one as a star/hub with it having connections to the remaining eight. Which topology would be more efficient for moving traffic between switches?
The original StackWise technology sent everything to the stack ring, and the source switch removed it. The later StackWise-Plus technology didn't flood the stack ring with all stack member traffic and unicast traffic was removed by the destination switch. Both huge improvements as you add stack members. StackWise-480 appears to be mainly StackWise-Plus with more bandwidth. It offers other improvements too, but you still run into the transit traffic issues of any daisy chain topology. That said, if you have enough inter stack traffic that this is a potential issue, you should be using either a chassis, with a switch fabric, or change your topology to non-stacked star. However, with stackable switches, don't overlook their proprietary stack ports often offer more bandwidth than ordinary Ethernet ports, so a small stack might still perform better than a similar star/hub topology with same number of devices. For even a large stack, is there enough traffic that there really would be a performance issue?
PS:
BTW, years ago, I worked in an environment where we had stacks of nine 3750Gs. Configuration changes, at the CLI, were slow, but switches seemed to always forward traffic correctly. This might have been because with StackWise and StackWise-Plus, one switch member, the "master", provides the "control plane" for the entire stack.
