Running process with grep-find interface is very slow

[Tom]

I often have to search large codebases and I use Ack for that
which is a better grep as it calls itself. I want to use the grep-find 
interface with ack, so I can jump to matches easily and it's working, 
but it's really slow.

When I run ack on the command line then it returns the
results in seconds, and if the files are cached by the OS then
it returns the results instantly.

But if I'm running the same command with the grep interface:

   (grep-find "c:/xampp/perl/bin/perl.exe c:/bin/ack -i somestuff")


then it takes minutes for the results appear in the grep buffer,
and when I'm running the same search again immediately when the OS
still have the files cached, even then it takes 30-40 seconds for
the results to appear.

Why is it so much smaller to run the same command via grep than
via the command line?


It's GNU Emacs 23.2.1 (i386-mingw-nt6.1.7601) on Windows.