i'm a packington user here.. love the bag for its spaciousness and classic design, not forgetting it's one of the very few billingham with a full zipper for greater protection... here's what I can stuff:
a) 5dmk2 with grip & medium zoom lens
b) 2 prime lenses on 1 side (35 f2,85 f1.8)
c) 1 long 70-200 f4 (hood inverted)
d) 2 x 430ex (1 on each side pocket)
e) 12" laptop slotted behind
f) the 2 front pouches are huge also and can squeeze up to 2 portable hard disks, with enough room for 4 sets of AA batteries, memory card pouch, cleaning kit etc.
Hope this helps