We are not going to have anything with more throughput than the 1544, it does L3 hardware ACLs and routing so you should get 1 Gbps throughput from port to port. Is there something in particular that is causing an issue?
The only thing would be the 1544P, since you had mentioned POE optional; and, POE cannot be an option if it isn't already available.
I would look into how the switch is being used and whether there is another issue on the network affecting performance. These have been very solid performers for us.
Anything suspicious under "show proc cpu" or "show memory heap"?
Are there particular interfaces taking a lot of errors? Possibly a duplex mismatch somewhere? Broadcast storm on the LAN maybe?
Specifically where does it seem to be running out of juice?
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