After careful mathematical analysis, which this comment box is too small to contain, I've determined that the optimal number of spaces for a tab is precisely 2e. Unfortunately, this turns out to pose certain practical problems. I imagine Plan9 came to the same conclusion and realized there wasn't a usable mathematical justification.
That still doesn't rule out evaluation by a proper artist. We just have to wait until s/he gets out of the Tufte Ashram(tm), bearing the answer on two golden ratio tablets, lettered in Helvetica.
