This strikes me as a very interesting option as perfect sound quality isn't a necessity. I know you touched on the sound strength, but what about clarity? Does the sound ever get too much static from competing signals?
Also, until this thread, I hadn't heard of the infinity kappas before but everyone seems to be bringing them up for a good stock locations replacement. I'll definitely have to check them out as I don't plan on adding speakers to any new locations. Do they make sizes to fit both front and back (A quick google search brings up the 3.5 front speakers but no 4 x 10 rear)?