IMO, a 6 hours cut means 4 more hours of unfinished special effects shots of people talking and walking in corridors.
We know Lucas was very concerned with the use of his money during the making of the prequels. He always said his goal was to make the most visualy amazing movie with the less possible money. There is no way there is a 6 hours cut of TPM around with plenty of finished special effects scenes. Well, I doubt it anyway.