I guess another appropriate question would be:
Does it make sense to even bother with vDS, or should I just go with vSS?
I should have problably mentioned that we will eventually be linking the 5.1 vCenter to another vCenter in another facility.
->It all really depends on your setup. If you use a lot of port groups (I use over 1000) then vDS is really great to make sure you sync configuration. If you use one port group and only have two hosts vSS is a lot easier. Vmware is putting a lot of time and effort development wise into the vDS and we continue to see improvements over time so it might be worth going to it to future proof yourself. Also since your paying for it why not use it. I'll see if I can help you with more upgrade steps a little later on.
Please feel free to ask more questions.
Thanks,