What I would do is finish work on the project, convert all the MIDI tracks and soft synths to audio, export that final audio mixdown, import it into another project and go to Process>Length. Set it to say, 85% and it will shorten the track, thus speeding it up without changing pitch. Undo if it's still not the right speed and choose another value.
Just read in the MC 6 Help file that it also works on MIDI. Not sure if it alters the tempo of the project, though.
Read more in the Help file.