Saddle height will be pretty close, but setback is less with modern geometry. The idea is to get the saddle forward and have better balance for tricky climbing. Handlebars vary quite a bit. Some people run a ton of drop, others have their hands as high as their hips. I’d say run the highest bars that you can still develop power.

Reminds me I've got to slam mine forward. I recently moved to an area with a lot of 20-30% climbs, and it gets super annoying having to put my nose down in front of the bars to get enough weight on the front wheel to keep it tracking. The whole longer-lower-slacker thing in MTB sure makes some things more difficult. (for the OP, keep in mind that "slack" to a roadie means seattube angle, but to a MTBer means headtube angle).

My saddle is very close to my road saddle position, probably a few mm back.

My starting point is to be able to stand on the pedals, lightly sit on the seat and have neutral weight on my hands. I'll adjust from there to get a good balance of front/rear grip.

When climbing I'll move my hands to the extreme outside of the bars to lengthen the reach (basically shortening my arms) and move my body forward. When riding flat or descending I can move my butt around to put more weight on the front or rear depending on where I need the grip.

This ^^^. I've got friends who ride MTB in the flat lands of Texas, some XC & some on 180mm travel Enduro bikes (my enduro buddies there are basically drunk BTW, lol). Here in the PNW, 10% minimum climbs are on the daily.

Flat land XC-MTB setup would generally be closer to road & no dropper seat post needed. Mountainous XC-MTB setup would generally be seat further forward, angled downward in the front on a dropper post with reach shortened & bars lower than a road setup, all to maximize power & grip when climbing & safety on the descents. I wouldn't think BB to effective seat height in any wouldn't differ from more than a cm.

FWIW...

Im in New England - so have some steep bits but not much sustained climbing local to me. My saddle had been nearly 2 cm lower and it had been like that for years with out noticing and that's what i'm familiar with - able to balance and climb the steep stuff. This last weekend going out with it adjusted up and I had trouble keeping the front end down when the trail kicked up. I'm thinking I need to go back to that climb and play around with the position.

That’s another beni of a dropper. You don’t have to drop them the whole way. You can take a little off the top and achieve whatever (lower) seat height you want. Generally you’ll find a seat height for best power, but as you noted, maybe your torso is out of position to keep from lifting the front w/the right seat height. This is where a longer reach (stem) and/or lower bars can get the most out of your bike for you. Easiest, if there are spacers under your stem on your head tube, you can pull some amount of those out. If your stem is flippable, you can do that as well to lower your bars. Adding reach will take either a stem and/or bars depending on your current setup. You’ll find your happy place if you stick with it.