I have to echo BrokenH's comments on volume 4. It really is a total cliff-hanger and waiting for the final installment will be very hard.
I have all the novels in Japanese as well, but am far away in my ability to read them. I believe it's been about 10 months now since vol. 5 was released in Japanese (I'll have to check my copy to confirm that), so I hope 2010 is a reasonable release date for an English translation, especially since the German translation is slated for Dec. 2009. Thank goodness my German is better than my Japanese in that respect!
When information becomes available, any updates on vol. 5 from June would be most welcome.