At least with today's version (8.0-pre release_8.0-pre-67-gd3361c), if I include a figure and then export to LaTeX, the resulting TeX file insists on including its own width specification, even when I tell it the width I want. For example, the org text

#+ATTR_LaTeX: :options width=1.7in
[[file:images/RS_head_cropped.png]]

results in the following LaTeX source:

\includegraphics[width=1.7in,width=.9\linewidth]{images/RS_head_cropped.png}

The second width specification (which I didn't ask for) seems to override the one I ask for, so the figure ends up a lot bigger than I want.