Installing 1000 files on a P5-233 machine took roughly about 1 1/2 ~ 2 minutes, but the progress dialog itself took about 4 minutes to finish. Basically, the installation of the files are already done, but it took a lot longer for the event loop to finish process all the events.
I do not believe that the problem is with the dialog/proxy code, rather the delay you are seeing is the time it take for finalize to complete. Please verify this by setting a break point at the end of finalize install. You will see that your breakpoint will be hit then (a few hundred lines later) the dialog will close. I would agree that the dialog does not give you an indication of progress during this stage, but I stand that the progress dialog performance is not a the real problem. If you care, please open up another bug which can address this dialogs shortcomings. I am going to mark as INVALID.
setting target milestone to M11 Need to get a copy of quantify to measure performance with and without UI dialogs, in order to define the problem.
So be it.
Bulk move of XPInstall (component to be deleted) bugs to Installer: XPInstall Engine