Thanks all for your replies.. So its extra fuel or extra piece of cake..
I thought we have a pretty basic configuration as I dont see anything that is not explicitely mentioned in the POH..I'll take a careful look at the equipment list to find the biggest offenders.
@tecman: the 580 vs 600 vs 620 MTOW is another mystery for me... I have 600 on the weight report. Have all the JFs been authorized to 620 or does it depend on a specific certification/serial number? I see sometimes metion to a certain "A12 addition" but have no idea what it is..