There's no limit that I've ever heard of or experienced.
We have 8 TB LUN and trying to over provision it as 72 TB with thin provision for testing purposes.
seems like a terrible idea. Why would want to over provision your datastore by 900%?
We are testing our storage products and over-provisioning is a MUST requirement
Well it's up to you, but over-provisioning of storage is always a dangerous proposition because of how quickly actual consumption can get away from you with no restrictions in place to halt it. At 900%, that's just crazy.