If you are only wanting to play midi and karaoke files do not waste your money on the G70 or Tyros 2. They do offer great playback of midi files since the sound engines in both are superb, but if you are miming over the top of them having spent over £2000 on either you'd have to be extremely rich or silly to be honest. All you need is a cheap keyboard that has a disc/hard drive to save your files onto. Maybe you'd be better offer getting a 2nd hand instrument or forget miming and get yourself one of the rack mount units with good gm/gs playback etc in it.
Good luck with whatever you have. If you simply must have a G70 or Tyros 2 take up keyboard lessons m8 and learn how to play those songs yourself, it's far more rewarding than shoving some disk in and pretending. Any musician in the audience will twig on straight away and realise that you are fake.