In an area as wide as the Piazza del Campo, a wide angled lens was called for. Accordingly, as for the last shot, I used my economy 9 to 18 mm. I'm sure that the Olympus pro wide angled lens would have performed spectacularly, with an extra 2 mm of width and F2 .8 of aperture, but the price was ridiculously over the top (and so was the weight, really) that the plastic fantastic certainly performed well enough.
I of course couldn't resist the temptation to create another leaning tower by using the optics of the ultra wide angle. Fear not, it didn't topple onto anyone.