Aux tanks? Maybe get the 6800kg increase first. Empty in Corp fit with deice will be close to 5000kg. Add two pilots, 5200. Add 4 stuffed shirts in the back and their 100kg of bags and you are at 5700 kg. 100 kg start and taxi, 200 kg reserve, leaves you one way VFR 400kg fuel, or about 120 miles at 145 knots.
Oh course you spent the big cash on deice so you could go IFR. Two approaches at 75kg, an alternate, and your range is about 20 miles. Go for the 6800 kg gross and you've got a reasonable 170nm. Don't forget all the flight planning limitations with the deice.
You are grossed out before a drop of fuel gets to the aux tank, even at 6800.