I'm pretty sure there's no good reason to upgrade at this time since we don't need the new features offered in 8.1
On the other hand, I'd like to stay up-to-date and I suspect that support for ESX 4 has been dropped only because VMWare officially stopped supporting it last month. It probably would still work under DP 8.1
Thanks for your advice. I've got the 8.1 software and new licences but I will hold on performing the upgrade