g1smd - 10:47 pm on May 8, 2010 (gmt 0)

Note that [A-Z] when used with the [NC] flag is processed twice as fast as using the [A-Za-z] pattern.

Note that /path-does-not-exist would redirect to the custom 404 error page if you have one anyway!

No. There is no redirect here. If you rewrite an incoming external URL request to fetch content from an internal server filepath that does not exist, Apache's ErrorDocument handler is directly invoked for that request. This is not a redirect.