Rofco B5 and B10 capacity

If you have a Rofco B5 or B10, I've got two questions for you:

1) PHG says the B5 has a dough capacity of 1Kg or 4.4 lbs. If I mix up a two loaf batch consisting of 1Kg of flour at 80% hydration and 20% levain, that's 2Kg or 8.8 lbs of dough. That means I would need a B10, right? What's the most dough you can really fit in a B5?

2) Does the 6" deck height ever become a problem? Like baking a large challah or tall rectangular loaf?

Thanks for sharing,
-Red