He goes over this in one of the podcasts, can't remember which episode. Jamil says that the default setting on the slurry tab is for rinsed yeast allowed to compact in the fridge for about a week. The max (4.5 billion/mL) are what you get from wyeast/white labs. I don't quite buy that your yeast is going to be 80% less compact than the white labs yeast, so I use somewhere between 3.5-4.5 billion/mL.
IIRC, Kai had a reference from one of those German textbooks of his of yeast cell count in slurry, and I thought it was to the high end of the mr.malty slider. I'll see if I can find the post...