I used to do this:

    emacs --batch --eval '(dump-emacs "em" "/usr/local/bin/emacs")'

This would load everything from your .emacs file into a fresh executable that would then start instantly.

Unfortunately, since I've done it last, it seems that this feature has been 'fixed' with emacs now printing that it can only be dumped once. Never had a problem with multiple dumping before.