This might sound rude but if you have to ask such super basic questions then you really shouldnt be going bush for "6 weeks at a time" .
Do you realise that if going for 6w you are going to be towing a trailer? So your car can carry 4litres/day water x 42 days =160 litres per person minimum? Plus 6w food, 6w fuel, which unless you are not moving at all is gonna be a conservative 1hour every 2 days so 24hrs driving worth so prob 300 litres fuel needed ,on top of your main there-n-back-again requirements! So with just fuel, food and water for 2 people you are +600kg.
6w at a time out bush isnt a detecting holiday but a serious odyssey requiring major planning in its own right.
Suggest start smaller like being no more than 2 hrs out of town, do 6 days and then back to town on the 7th for a pub meal & restock/sanity break. If you can do that 6x back to back then you might be ready to do 2-3w. After a couple of those you will be ready for 6w knowing what you NEED to take and equally important what you really dont need at all. You will answer your own question
The only detectors you should consider are the 7000,6000,5000,4500 and 2300 as these will def handle the ground. If they cant then nothing will.
If you are swinging 8 hrs a day then the 6000 is by far the most attractive but if you have to ask the "which detector" question then unless you hit the motherlode then you wont be spending 6w x8hrs at a time detecting as no-one goes from not having a detector to Pro level hours in one hit.
Love your enthusiasm though.