Ken has it correct.
I'd add that execpt for when you want to "rail" your new board to really get upwind (placing your weight slightly off center on the downwind side to roll the lee rail down a little bit) fast, with the CB all the way down, you should try to keep it as up and stowed as possible.
Ken's points on using it for stability are correct as long as the board is moving along well.
Standing still the CB does very little toward increasing stability (it's not a "weighted at the end" keel).
The reason for keepng the mast foot as far forward as it will go, to head upwind, is to increase the waterline length.
When you are subplaning (in displacement mode) the longer the waterline length, the faster the board will move through the water.
If you have a bit more wind and speed, the longer waterline length gives the board a little more "bite" to keep it tracking upwind.
As Ken suggests, you need to be very aware of your fore and aft trim.
Do not get the nose too high as this will cause drag, and don't get the nose too low as this will have the same effect.
So as your speed increases, you can move back a little further on the board, progressively, and your speed increases/progresses.
Rail to rail trim is important as well.
Ken has given you all the correct theories, now you just need to get out on the water and practice them, modify them to suit your board, your rigs, and your size/weight.
What rigs are you using.
I would suspect from your closing comment ("Uphauling wears me out") you are falling into the water more than necessary, your uphauling technique could use some work,
or your sail/mast/boom (the rig) is way too heavy by modern standards.
Hope this helps,