My experience with demo'd spots is they are typically pretty trashy. Not necessarily tab rings and tails, square tabs, foil and bottle caps trash, but nails, big iron, copper and brass. Hence, the 5 x 8 would be a better choice then the 11". Nothing, seemingly, should be all that deep, either.
Also, you might be surprised on the silver coins. A couple years ago I hunted a airport flyway zone where houses from the early 60's to late 70's were demo'd back in the late 80s'. Over about a year and a half time span I ended up recovering over 100 silver coins from the spot and my hunting buddy had a decent number as well. We kept all the copper and brass, too, and got enough to write out a check to the local dog rescue for $255.00. There was good numbers of clad and several nice jewelry recoveries, too.
Anyway, not intended to hijack your post, but merely to point out some housing development demo'd spots can be surprisingly good....in several different ways.
If there is any way to discern where the driveways were, those along the side and curb strips held the majority of coins. However, the majority of the jewelry came out of the yards. Good luck, and let up know how it goes. HH jim tn