I have done this exact swap out, one thing you must look into if its on your network is multicast traffic,Specifically layer 3, Meraki switches functionality is vastly different as they will use the dataplan of 1 switch for a entire stack (remember 6500's have Sups that handle the grunt), so if you had layer 2 line cards in your 6500 the same replication would not be that simple.    Example:  If you had 3 x line cards with 48 ports on each, all that have phones connected for example. This would not be as simple as moving these over to a stack of 3 x 450 Meraki switches as 3 x 48 ports of data would travel through one 450's processing power.    You will need to outlay your requirements and potentially split your original 6500 into 2 stack of 450's to balance the data that spreads across them, or run a distribution layer and a access layer in turn avoiding this issue altogether. I hope that has helped!.  ... View more