the f3x is really great and probably the most versatile bag I've seen so far. The strap is much better than the F6 strap, which is too narrow for my taste. The f3x swallows a lot of gear if needed, but somewhat doesn't look too big if only half loaded.
The bag comes with one separator dividing the big compartment in two. One short domke insert for two lenses fits very well in one of those, so you can easily have one body / lens attached plus four more lenses (not stacked) in the main compartment, as the main comp already got two lens pockets.
The only downside I found is, that the main flap is not really protecting the interior against weather inconveniences, as it leaves a smaller opening on both sides, if not careful. In heavy rain or very dusty environment I'd chose something else, probably.