I'm posting this reply in hopes it will help someone else. Why support never could verify my license over 2 days I have no clue, but they could not, and kept asking me to resend it (I even sent screenshots of my license page at my.vmware.com).
I used this KB article:
..and selected just 2 CPUs to upgrade. It worked great, and my new install of 5.1 took the new 5.x key.
The only odd thing is that, it generated a new key for 4.x <-- I did not need this and did not select this. My two 4.x hosts are working just fine. I have no plans to muck with my existing 4.x hosts and their key to input this new, 4.x key below (where it says, "vSphere 4 Essentials:"). I mean, why is it even doing this at all? The main reason I posted here at the forums was due to the odd/scary "Attention" warning, that seems to indicate I must muck with my existing 4.x hosts and their license keys.
Here is a screen of the results:
