XML Performance in a Transacation

This is a pretty general question, and I know that it can very from 
application to application, and even from parser to parser.   However, 
I'm curious if anybody has any links to some performance tests that show 
the overall time a transaction takes to complete, and how much of that 
overall transaction time is devoted to parsing or validation of an XML 
file.   Particularly, from retrieving an XML file from a data store, and 
then completing the end transaction.

I've been requested to provide some numbers to show that actual XML 
validation results and parsing are a small portion of the overall 
transaction process, when dealing with XML in a B2B process.  Any 
information that can be provided would be appreciated.

Dave