One thing not yet discussed is call handling capabilities. That is: calls per second. My company owns several DX gateways in London for VoIP –> Q.931. If you throw calls at the gateways, the call setup times can be as long as 10 or 15 seconds, whereas, normally, calls are set up in one second.
I have not managed to find any published figures for calls per second on the DX gateways, but my experience is that a DX-4120 can handle about 10 calls a second before it begins to slow down.
Anything faster tends to come from call centre customers with autodiallers, so we simply implement call gapping on our switch for those particular customers to get round the problem.
The answer may be to use a Quintum CMS, but I doubt it. And I have never used a Cisco gateway, so I do not know how they compare with the Tenor.