Hi Carl ,
What is your Switch Hardware for your new distribution switches , Stacking is mainly meant for doubling your switch bandwidth .
What is your traffic load from your user access segment . Do you see huge traffic where single hardware cant process your traffic ??
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Cisco StackWise technology provides an innovative new method for collectively utilizing the capabilities of a stack of switches. Individual switches intelligently join to create a single switching unit with a 32-Gbps switching stack interconnect. Configuration and routing information is shared by every switch in the stack, creating a single switching unit. Switches can be added to and deleted from a working stack without affecting performance.
http://www.cisco.com/en/US/prod/collateral/switches/ps5718/ps5023/prod_white_paper09186a00801b096a.html
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On Distribution layer its always better to run on HA mode with Gateway redudancy protocol .
HTH
Regards
Santhosh Saravanan
HTH
Regards
Santhosh Saravanan