Kevin B. and Daniel Tn...
Let me give some thoughts here, that might be of some use.
First, on battery life...it is pretty bad, indeed. I had an F70, and like you said Daniel, it would run forever and a day on those double-A's. The life with the 9V basically stinks. The one way I have come to look at it though, is -- it IS only one battery; before, in your F75, it was four of them.
Now, as for depth -- is your soil very dry, Daniel? You are definitely a bit more mineralized than I am; I don't usually have that many "bars" on my Fe meter, but I DO ground balance in the 50s most times, and I DO have very, very red clay here. But -- dry soil KILLS depth. It's not just the Gold Bug. I have a Minelab Explorer SE Pro -- and I have been testing coils in my test garden (which is now VERY dry.) The depth with this thing STINKS right now. I cannot even get a PEEP out of a 10" dime; an 8" dime will give an occasional hint, but it is in NO WAY a diggable target. Last night, I re-ran my Gold Bug through the garden to compare, as I had some pretty detailed notes on how it did back when the soil was moist. It is DEFINITELY not hitting as deep right now -- but that is normal for dry soil. Further, if you will believe it, my Gold Bug -- even given that it is not hitting coins as deep right now -- is actually DEEPER than my SE Pro. I could get, last night, a very-close-to diggable signal, maybe I'd even call it "diggable," on that 8" dime, that was NOT diggable on the Minelab. It was not a GREAT hit, but it was a bit better than the Minelab on that same coin. Likewise, I could get at least a peep out of my 12" quarter with the Gold Bug, and a little better on the 10" quarter. With my Explorer, the 12" quarter was TOTALLY silent, and the 10" gave peeps, but was NOT diggable.
I would say right now that I have roughly about 1" more usable depth with the Gold Bug than with my Explorer. And, still, I have probably 2" less "usable" depth right now with my Gold Bug than I did back when the soil was moist. I would definitely say I have lost a good 1 1/2 to 2". But, I don't think you can hold a "decrease in depth due to dried out dirt" against the machine. Most machines seem to suffer in dry ground (I KNOW my Explorer is -- so much so that I thought it had a problem -- so I borrowed my friend's SE Pro...and when I tested it, it gave the EXACT same performance).
One other thing I'll add is that my digital ID is also suffering right now in this hard, dry ground. MUCH lower, jumpier, and less accurate numbers than I was getting when the ground was moist. I am now getting alot of mid-range numbers on the deeper coins; on the real deep ones, I was getting alot of teens, and only occasional higher numbers in the 80s. On that 8" dime in particular, I was getting alot of low 70s readings as I recall, MUCH lower than it should be, and MUCH lower than I was getting when the ground was moist. It's simply the ground conditions.
Finally, Daniel, about your hunt at the school today. A 48 ground balance, with 2-3 bars, is similar to some ground I hunt in here. You should be able to hit a coin MUCH MUCH deeper than 3-4". Now, NO, they do NOT hit with that very LOUD signal that you get on a shallow coin. It definitely is a different kind of tone (the way a deep coin hits on the machine). It's definitely a "softer" sound than the shallow coins. But it is SUPPOSED to be that way. These machines are "modulated" audio, which means a shallow coin hits LOUD, and deeper coins hit quieter -- it's actually intended to be a GOOD thing -- in that you can get a sense of "depth" of your target without even having to look at the depth meter. Some people don't like it -- and would rather have "saturated" audio (audio that sounds "loud" no matter HOW deep or small the target is). Once, though, you get used to how deep coins "sound" (in your test garden), then in the field -- when you get one of those types of hits that is repeatable in a couple of directions, you will know to dig it. You WILL start getting deeper coins.
I hope this is somewhat helpful, and might answer a few questions. Oh -- on the pinpoint/depth issue, I don't find that my 11" coil is THAT bad; it's not TOTALLY accurate on the depth, but it certainly doesn't read everything as "0". The only question I will ask is, did you BUY your machine as the "DP" model with the 11" coil, or did you buy it with the 5" coil and then ADD the 11"? Reason I ask is, I wonder if the "DP" models, which are simply a "Pro" with an 11" coil as the standard, stock coil, I wonder if they "calibrate" those based on the coil they come stock supplied with -- i.e., the Pro's depth is calibrated for the 5" coil, and the "DP's" depth is calibrated for the 11"? Just speculating, as I do not know that.
Hope this helps some...
Steve