I've got enough experience with this now that I feel comfortable drawing some conclusions.
-despite my initial thoughts, IMHO 10" is just too much mounted in that location. There have been a few instances where I can't see curbs (or rocks!) when making sharp turns. Unlike the round profile of the lights on the hood, this is basically a brick wall; there's no seeing around or under it. I cannot recommend going with a 10" screen up top like I'd initially thought would be ok.
-a 7" screen is much more manageable. In fact, unlike the 10", there was never a time that I didn't see whatever was there; yes obviously you're giving up visibility with anything up there, but the 7" form factor was very workable with a slight side to side head movement. If you're considering this, stick with something this size or smaller.
-in terms of software functionality, this setup rocks. I ended up using BackCountry Navigator for off road stuff exclusively. This app has emerged as the best, by far with its recent addition of AccuTerra maps as a source ($20 one time charge for unlimited maps). These maps blow anything else currently available away, and that goes for any GPS with topo features.
-on the 4k mile round trip I took for the TRR, I was reminded how much better Goggle Maps is over CoPilot or Navigator. In fact, I ended up wirelessly tethering the tablet to my phone, and then using Google Maps that way for most of those miles. This worked surprisingly well. Bottom line here is that CoPilot and Navigator work, but I've been spoiled by Google Maps. Fortunately via that wireless tether, I can keep using Google Maps, and only fall back on the other two options if the intertubes die or something.
-Now for the biggest issue; in fact IMHO this is a show stopper that makes this entire approach *for offline off road navigation* a fail... the position of the tablet has it right up front, in full view of the blazing sun. Even with the AC blasting, temps at the back of the tablet, where the battery is, got so hot that the thing shut itself off. And it stayed off. For a long time. Every time I tried to restart it, it wouldn't have any of it, saying it had overheated. Eventually it cooled enough to restart, only to overheat again. Not good.
So, I think the bottom line for me is that this is *exactly* what I was hoping for, you know, except for the whole overheating-and-not-working-at-all thing. I can't suggest you replicate this setup. Not unless we can find a tablet designed for harsh enviornments. Something that won't shut itself off or overheat in the first place, and hopefully something that has a better/sunlight readable screen. The little checking I did says I'm about 2 years too early for that though; current solutions seem to be $1000+ range.
Wish I had better news to report
. As of now, I'm back to using my phone, keeping it in the shade.