Tamron 17-50 vs Nikon 18-70

One of my first lenses was a Nikon 18-70 which I got as a kit lens with my D70s. It was a great lens, especially for that price. But for a long time now, I've been looking for an upgrade, something in f2.8 range. I looked around and while there are lots of options, I didn't really like any of them. Nikon 17-55 was the best one, but the fact it's designed for DX body, didn't make it a sensible purchase. So I turned to the next best candidate, Tamron 17-50.
It got good review almost everywhere I looked, so it made a great candidate to test it out. So I did. Got a copy from the importer yesterday and started with some basic focus and sharpness tests. I think it's safe to say, Tamron is in deed sharper then Nikon and it looks like, I got a good copy as well, it's sharp even totally opened. So all good then, right? Well, not quite.. I found a strange "problem", that I can't really explain. It's about dof (depth of field). Nikon has A LOT more dof at the same settings as Tamron has.
I have to test this a bit more, but it's beginning to bother me. Or not.. In a way, this is good news if you like shallow dof and bokeh is nice as well. But not so good if you want deep dof and lots of sharpness.

Some pics from both, compared in Lightroom.
Don't look at the sharpness in these, all saved using Save For Web function, so compression is quite high.

24mm, f4


35mm, f5.6


50mm, f5.6


50mm, f11
Look at my printer cover, you see texture with Nikon, nothing with Tamron.