Originally posted by robgo2 If IQ is your top priority, then the answer to your question is clear: Get the FA43
I don't think a 43mm is really a clear answer to someone looking for a lens a good bit wider than 50mm.
Your suggestion of the 31mm 1.8 ltd was a good one, but it's kind of hard to make a case for it when the lowest price online is $989.95 (Adorama), and the excellent Sigma 30mm 1.4 can be had for less than half the price at $454.99 (42nd Street Photo). Not to mention the fact that the Sigma is 2/3 stop faster.
I have the Sigma, and I do spend a lot of time at f1.4, so I would definitely miss it. With a wider angle like the 30 or 31mm, you need to use a very large aperture to induce bokeh in lot of situations, so the 1.4 is very useful.