In my test lab, I have one Dell r610 with 2 6 core processors and 24gb ram. Running on the server I have the following.
Avaya Simplex Servers
Avaya Duplex Servers
Avaya Aura Messaging
WebLM
Utility servers
Presence servers
Enablement servers
I might be forgetting some others.
I have multiple of each one for different testing I have done in the past, all of these work very well on this server. I also have on my workstation running vmware workstation with System Platform installed and some templates installed on it for testing. (System Platform will not install correctly in ESXi, so I had to use Vmware Workstation)
In total I have about 25 - 30 VMs running on this sever. Of course it is not on 24/7 as it is only for learning and testing.