Overhead of using Panels Panels is one of the most useful modules for Drupal and many websites make use of it.
However I always have been cautious using it because of its processing overheads.
I want to know is there any benchmark or article about Panels efficiency on the net?

Thank you.
This is the only thing I recall seeing, at DrupalCon San Fran in 2010. Sam Boyer, a maintainer of Panels, discusses benchmarks a bit in this video:  http://sf2010.drupal.org/conference/sessions/state-panels-3-and-more-what-you-love  at about the 29 minute mark.  It's not really a great benchmark test, but gives some idea into what page manager is running/processing.