tweaking under repeatable load

[Ben <bench@xxxxxxxxxxxxxxx>]

I'd like to optimize my postgres configuration for optimal  
performance under typical load. Unfortunately, as I understand  
things, that implies that I have to have a way to repeat the same  
load each time I try out new settings, so that I can fairly compare.  
It's difficult for me to drive the load all the way through my  
application, so I'm envisioning some script like pqa that analyzes  
the logged queries against the database during a typical load period,  
and then lets me replay them directly against the database with the  
same original frequency.

Has anybody done anything similar to this? Anything better? Did it  
end up being a waste of time, or was it helpful?