would something like the sigma 18-50 f2.8 yield better results than the 16-85?
I'd substitute the Sigma for the Tamron 17-50, but yes.
The 16-85 - while a good lens, is f/5.6 at 50mm. Thats two stops slower than the Sigma or Tamron, and in bar you are going to have moving people. For this you need a wider aperture, not VR.