Oh heck. I typoed exactly the opposite of what I meant to say. Of course I meant that little liquid with extract, not all grain. Doh!
At any rate, I'm learning to ignore the extract recipies on the subject of water levels.
The only water level that matters is the one at the END of boiling.
You can dump your extract into 100 gallons of water, and then boil it down to 5 and be fine. (OK, it will caramelize a bit more, darker in color, whatever, it's hyperbole).
If you are ending up with 3 gallons at the end, then start with more water! Learn how much your pot boils off, and make sure you start with enough water to finish your boil at 5 or 5.5 gallons.
Oh, and I vote for the 16 gallon pot too. I have just gotten a few batches under my belt with my 16 gal keggle, and LOVE IT. Double batches are a great way to get ahead with a pipeline too!
(This is, of course, if you have a pot that can handle a full boil, which typically means a 7.5 gallon or larger pot. If you have something smaller, then boil as much as possible, and top up with boiled water from another pot...edit, reread your post and see that you have a 10 gallon pot. USE IT! Start with 7 gallons or more of water, whatever you need to end at 5.5 or 5 gallons.).