Very easy to organize the padding. The medium accomodates my d300 w/medium-sized lens attached, 80-200/2.8, 105VR, 85mm/1.8, 50mm/1.8, sb600, su800, and lightsphere. I'm sure you could fit 2 bodies, but a. I don't have an extra body, and b. I like to carry my camera with the tamron 17-50/2.8 attached. It fits all of my current equipment.
I haven't used the large bag yet, but seeing how heavy the medium is loaded, I'm sure it's a blessing to be on wheels. Should hold approx the same equipment plus laptop. Bag is much taller. Only complaint about the large bag is it looks like it is leaning forward due to the wheels, but that's not a big deal.