Here is an interesting article on the impact of the latency on some usual Oracle SQL statement over Local, LAN and WAN networks.

http://markbairden.blogspot.fr/2012/03/database-performance-measuring-effects.html

Wan latency uses is 12ms which is small for this type of connection. Impact is huge with a factor of 10. To be taken into account in your designs !

Thank you Mark for this article !