Any EC155 drivers ?  

You will get the same fuel burn rate, for the most part, with 2 pilots 0 passengers as you will with 2 pilots 5 passengers. Someone may disagree with me but they are trying to look smarter than they are. The bigger difference in the weight increase will be a drop in cruise airspeed. With the increase in weight you will see a drop of up to 7 knots cruise airspeed at the top end of the green.

You should be able to get 3 hours of flight coming out of an airport at max gross weight. It may be a little tougher coming out of helipad but if you are patient with the takeoff and let the aircraft do its job it will get off the ground. Some pilots are not patient and want to jump off the ground on every take-off no matter the aircraft weight, temperature, humidity and winds.

Hope this helps