Where to download ESX5,x for HP DL380p G8

Hi

The customer allready has one ESXi 4.1. host (ML350 G7 one CPU).
We manage this ESXi via vSphere Client.
The client has purchaced these VMware licenses:
- VMware vSphere 4 Essentials Bundle for 3 hosts (Max 2 processors per host and 6 cores per processor)
- Subscription only for VMware vSphere Essentials Bundle for 1 year
- VMware vSphere Essentials Per Incident Support - Email + Phone, 1 incident/year

Now we are installing a new Vmware host to DL380p G8 with two CPU (6 cores) and SD-card for ESXi boot.

We are planning to manage it via vSphere Client too - it is not extremely important to consolidate this installation to old ESXi 4.1 installation. But if we gain something good by doing so please hint. In that case we propably have to upgrade old ESXi 4.1 hos to to ESX 5.x, right?

Where should we download the ESX and which version you recommend. I believe that we should download ESXi from HP's webpages.

The first VM will be a SBS 2011 std (migrated from old SBS 2003 / ML350)

Thanks,

Juha