Hi Roberto,
Please see Release Update (www.dialogic.com/.../release_update.pdf) section "1.51.1 Configuration and Performance Recommendations" and it has minimum recommended system spec for high-density systems.
With respect to Virtual environments, please see 1.72 Virtualization Support in the same document and it has few recommendations. We have separate document on VM Optimization (www.dialogic.com/.../XMS_VMOptimizingAppNote.pdf) as part of XMS. I believe it also applies to HMP4.1 when using in virtual environments.
I understand it is not giving you all the details that you are expecting. But, at least it will guide you what kind of hardware you need and how to tune VM settings. Hope this helps.
Thanks,
Sunil.