OK, I think I know what the answer is going to be for a few reasons, but I thought I'd ask...
The older ZA 16-35 f2.8 is bigger, 2x as heavy, and a stop faster (which explains the size and weight difference).
It also has a closer focus distance, higher maximum magnification, 9 blades instead of 7 in the aperture, more distortion, worse chroma (especially at the wide end), etc.
It's not a perfect performer at all, and comparisons at dxomark indicate that the FE version of this lens should be the superior lens in most respects... but not necessarily all. Bokeh and waveform distortion, is not clear, but it appears the FE is worse for the distortion.
However, it is faster, and if you shoot in the f8-11 range, they both may perform similarly in terms of sharpness.
Plus, it will fit on my a900, which I am still very happily shooting. If I buy the new FE lens, that will likely mark the beginning of the end of the a900 for me, and I'll probably sell it along with the wides that this lens will replace.
I looked around and didn't see any comparisons online, so I'm hoping someone out there in the ether can comment on this from experience, and any examples would be lovely!