[Rob Neilson] "I've just attempted another output and discovered the drift is inconsistent? "
then there is something in your project that is off.
is it completely rendered? and the audio mixed down?
have you tried using the final as a self-contained movie? usually the issue falls somewhere in the storage's ability to access assorted files that have been rendered across the array.
gary adcock
Studio37
HD & Film Consultation
Post and Production Workflows
Inside look at the IoHD
http://library.creativecow.net/articles/adcock_gary/AJAIOHD.php