Upgrade question - Nikon 28-70/2.8 to Tamron 24-70/2.8 VC?

As I continue to build out my FX kit, I am re-examining my lens inventory.  I have a good copy of the Nikon 28-70/2.8.  It is one of my favorite lenses.  Yes, it is huge and feels like a brick but it delivers, both resolution and color rendition.

My reason for posting is 28mm just isn't wide enough generally.  I could overlook this with my DX kit since the 28-70mm never was intended as a DX lens.  But as I continue the transition to FX, I continually find myself cranking to the 28mm and trying to figure out how to adjust.  I have the Nikon 24-85/VR kit lens.  It is OK but just doesn't have that extra "pop" that the 28-70/2.8 can deliver.

The 24-120/4 doesn't really interest me (at least for the price) and I can't really afford or justify the Nikon 24-70/2.8.  Which brings me to the subject of this post.  Is the Tamron 24-70/2.8 VC a viable upgrade to the Nikon 28-70/2.8?  I figure that I could probably sell the 28-70 and 24-85/VR and come about even, maybe a little better.

Saying that, I almost shudder when considering Tamron.  My past experience has been hit or miss.  When you get a good copy, they are great and when not...just a source of frustration.  I have read that the 24-70/2.8 VC is supposed to be built to a higher standard than their usual consumer grade but still skeptical.  Still if it can provide equivalent performance in the 28-70 range and provide the extra angle of view of a 24mm, then I am interested.

Anyone have direct experience with both lenses?  Opinions?