So, here's a weird one. I suspect our group is screwed, but we have a series of servers that are in testing. They got basic ESX free licensing because most of these hardware systems are going to be ...

I don't know if this is limited to paid keys, but for my Enterprise keys I can convert from 6.0 down to 5.5 or 5.0 and back up again if needed. I do have active support, so that's possibly part of it.