Have you tried nice_find?

http://github.com/briancollins/nice_find

It's a plugin, not a bundle (like Ack In Project) so it feels native, it is asynchronous, and it uses git-grep when available. I love it.

I love you.

Ack in Project to the rescue:

http://github.com/protocool/ack-tmbundle

Sure, it's not the native find in project, but it's way faster. Not a day goes by that I don't use it.

I run into that all the time. Even opening a big file takes TM to its knees. I keep TextWrangler on the Dock for when I need to open big files or search large projects.