I'd personally kill for a 20-70 range with solid optics. 20-40s could be a bit of a stretch shooting event portraits, but probably doable with some cropping in post. 24 just really isn't wide enough quite often.
I had the Tamron also and it is fantastic. As excited I'd be about this lens I wouldn't have parted with the Tamron. This will probably come in at $1,999 at least