Thanks, if it was the CPUs only I would have concluded the same indeed!
Here though there's a new motherboard and different brand too, still supporting Opteron CPUs but I would expect some drivers to be different.. not sure?
The drivers will certainly be different. If you are patient to reinstall Esxi, it is safer.
If I were you I would do it, and if possible, with some more updated versions, even 5.5 or 6.0