The build is not the issue, it will prob be the amount of flaring, CA and purple fringing. It should be sharp at all apertures except wide open, and you should see improvement in IQ when stopped down a bit to around f/2.8. Also the AF speed should be really fast and accurate. If it performs better than all this you have a great copy, if not maybe you could swap it for another one.
Don't be shocked if it doesn't perform well at f/1.8, though it should at least be useable.