Oly user making the switch... need advice on wide-normal zoom.

Hi everyone.

I've been a happy Olympus user since my first DSLR 4 years ago. The High iso performance and improved DR of a d7000 over anything Oly has to offer is becoming a serious draw.

I've looked at the switch before, but have never found anything with the versatility of my 12-60.

My current kit consists of an

e-620 body
2 x E1 bodies

12-60mm (24-120 in 35mm)
50-200mm (100-400 in 35mm)

Does anyone have experience with the Nikon 16-85 vs. the Sigma 17-70? Are there other lenses I should be looking at?

Thanks

--
-Sadim
http://foundacuity.blogspot.com