Depends on how heavy the traffic is coming off those 6509's . The 3750's have like 32 gig per second backplane capacity. If you have a lotof traffic you might want to think about something a little more robust like the 4500's series. You should try to get some monitoring statistics for all those switches and see what kind of traffic you are looking at. It's a expensive decision you have to live with if you get something that's not up to the task. It also tends to tick off the higher ups. :-)
You would need to ask Cisco what they recommend, but likely they would suggest another pair of 6500s.
However, from what you describe a dual stack of 3750Gs might be just fine as well as a pair (although if you use a pair, not stacked, you might consider the 3650G).
As Glen notes, expected resource demand is a consideration since the switch's fabric is "only" 32 Gbps, but there's also its PPS to consider too. Further, in a stack configuration you need to consider that limitation of the ring bandwidth (NB: the 32 Mbps ring is really dual 8 Gbps duplex.) All of these considerations, though, I suspect would not be an issue for what you've described.
Within the 3570 series, the 12 SFP port 3750G-12S offers SDM templates not available in the other models which can be useful in a distribution or core layer role (BTW, if you mix this unit in a stack with other models, you can't use the additional templates.)
One advantage of a stack, you can Etherchannel to different stack members which might avoid some uplink usage issues working with a pair of devices.
If there was a need for additional performance, there are other possible platforms besides the 4500 and 6500 chassis. The 3560-E, 3750-E and 4900 series could be considered too.
We are pleased to announce availability of Beta software for 16.6.3.
16.6.3 will be the second rebuild on the 16.6 release train targeted
towards Catalyst 9500/9400/9300/3850/3650 switching platforms. We are
looking for early feedback from customers befor...
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