Good point about the emergency brake, I was not considering that when I first posted. Mostly because last time I lost brakes was in a 10,000 lb truck without an emergency brake. I was getting off the interstate and was able to down shift and get stopped in a parking lot without incident, but not much fun...
I often tow things, the emergency brake is not as good as 4 wheel brakes, and could still leave you in a pickle.
Some emergency brakes are better than others too.
Think about the time required to realize what is happening and grab or press the emergency brake.
Also consider the other people out there. If you stomped on your brakes to avoid someone else being stupid your brakes could fail right then, and it's to late to think about the emergency brake...
I think that for most everyone there are still several times in a week that my "question" could not be answered with a good emergency brake.
I do think a single circuit brake system kept in good condition can be as reliable as a dual circuit system. On the other hand a dual circuit system will always be safer, you can't argue that.
Everyone must make there own decisions, but for a daily driver that is not bone stock I still say dual circuit is best.
Grigg