development / tests system and production/simulation systems are geographically located in different places and hence the /usr/sap/trans is located at the production systems.
In this case what should be the Wan speed recommended in distributed SAP installation for the NFS mount?
Is there a note, document or tool to evaluate the architecture?
I don't know any documentation regarding this, as it's highly dependent on your usage profile of data interchange between the systems. Consider the load of following maintenance activities (list is not complete): pure transport load, client copies (RFC or TMS), system copies (backup/restore infrastructure), support packages, upgrades, connection to central systems (SLD, SolMan, Portal).
Due to this generally I would not advise to separate systems of one landscape into several datacenters without proper reason.
On the other side if you have to do so, I think /usr/sap/trans will not make any problems with midsize enterprise WAN connection (>= 2MBit sync.). But you will have to bear in mind that connection could be slower if you need to transfer more date (e.g. syscopy from P to Q). Best will be : set it up, test it, and for the case that there will be any problems save the possibility to enhance bandwidth afterwards.