"use version 5 to update existing projects"
Sure. But if I update them in Keynote 5, I can not present them reliably with Mavericks. (I am sure it is common knowledge now that the VRAM-memory glitch prevents that.)
If I only had known better, I would have never updated my PowerBook to Mavericks, but when it was done just figured out that I will update my presentations to Keynote 6 and solve the problem this way.
What I should have done – and I recommend this to every one with the same situation (huge amount of complex presentations) – is downgrade back to 10.8 and work in Keynote 5 and re-consider the situation, lets say after 2015.
Now I just rework every other slide from scrath, I can not do it anymore, since 25 % of presentations are already upgarded to 6. Huge amount of otiose work.