Speed on Windows for big repos

[Adrian Buehlmann]

The relative speed of Mercurial 0.9.5 on Windows XP compared to on Linux seems 
to be rather weak for big repositories:

See the Netbeans repo test runs on:
http://www.selenic.com/mercurial/wiki/index.cgi/RepoSamples

   Files: 74'713
   Changesets: 64'888
   Total Revisions: 325'131

Local "clone --pull":

   Ubuntu 7.10 on Core 2 Duo, 2GB RAM:             260 sec (< 5 min)
   Windows XP SP2, 2.4 GHz Pentium 4, 1 GB RAM:  4'150 sec (> 1 h  )

Ok, not the same hardware, but a factor of nearly 16?

I did the Windows run using the batteries included installer (thanks to Jesse 
for posting the Ubuntu test data). Windows CPU load was rather low, peak memory 
usage far below 200 MB. Per my personal paranoia, I suspect that hg was mostly 
waiting for disk writes to complete.

Why is Mercurial on Windows really that much slower than on Linux?

How could this be improved?