As a quick and dirty test I tried running both Command-T and Ctrl-P against a directory tree containing some 26,000 XML files. Command-T takes roughly 10-15 seconds to become responsive. Ctrl-P chokes and requires a Vim restart after invoking it against this directory.
Is there a reason that Ctrl-P, FuzzyFinder, and Command-T choke on large directories? On windows, I've used this piece of software called Everything Search that seems to index the entire filesystem (say around 30,000 files) in under 5 seconds. That's really impressive and I love using it for that.
But it makes me sad to use these vim extensions choking on directories of similar size. Maybe NTFS vs ext4 has something to do with it?