I can answer a few of those questions. I had a Cortes a couple of years back, so I still can remember most of what you asked.
First, you stated the ground balancing nuances correctly with the Cortes. That was my biggest complaint with my Cortes. I would have really enjoyed using it if it didnt false and chatter in our highly mineralized soil conditions. I could have used all metal mode, but I didnt want to listen to it beep over any nail or hot rock as well. You probably wont have that problem though, in nice soil. I took my detector to Illinois, right after I got it, and it worked nice and smooth in all modes.
Second, the notch. I didnt use the notch much. I tended to use the numeric readout as my notch. The tabs tended to be in a pretty tight range in a couple of different zones. I typically dug anything regardless, but if I were feeling lazy, and I saw a reading of 43-46, I knew it would be a tab. The notch feature allowed you to select a narrow or wide notch range. It didnt allow you to slide the range up or down, just how wide you wanted it.
The Sum mode was something I didnt use much. The only time I really used it was when I had a reading that jumped between a higher number (80's to 95) and zero. If you pushed the sum tab,(it is spring loaded, so that you cant keep it there) it kind of averages the numbers and presents it in a tone. I think there were 8 tones. If the numbers were jumping between high and low, and the tone was low, it was alway a rusty nail(in the few instances that I chose to dig). I stopped using my sum mode, because of an unusual quirk, in that it (the detector) would often reset itself. By that, I mean that it would quickly shut off and then turn itself back on. That was a little annoying. I never heard anyone else complain about that on the forum, so I assumed it was just my detector.
I guess the depth would be pretty much typical of the previous generation of Tesoro detectors. Although I didnt see much difference between it and the Tejon that I traded it for. It will probably do just fine for you, if this is the detector that your looking at.
Overall, I like the detector. I thought the Tejon would be head and shoulders above it, so thats why I traded mine. A few tweaks from Tesoro, and it could be a excellent detector. Best of luck in your decision, and I hope this was more helpful than hurtful.
J.