the F3 is a super Under rated bag. based on my own experience, there is really alot you can fit inside it (if you arrange them well)
the heaviest i tried?
main compartment: 30D+Grip+17-40L (attached), + 50 1.4 and 85 1.8 (stacked) + 135L (barely fitting inside the divider slot) + GF LS II
side pocket: 580EX (1 side) + a small story book
small compartment near buckle area: 2 CPLs + blower + lens pen
That is quite a load! Wow now i'm really considering that bag.