I think we really have to wait and see what the new Sigma 50mm f/1.4 Art has to offer. If word through the grapevine is correct, then it'll be a contender with "Otus" caliber IQ. If those reports are correct, it will also carry a price tag that'll be higher than you'd expect for a Sigma lens in that category but certainly lower than that of the Otus's.

Only time will tell how much incremental value the Otus's IQ and build quality have. Right now, though, it's in a class of its own.