No companion core in the S3. The reason it saves juice is because it runs the two cpu cores at different speeds and despite what Nvidia publishes that's an advantage that the S3 has that the A9 Cortex does not.
As far as not as good as the 4460 overall - that will have to remain to be seen and how you use things. The S3 at 1.5 GHz cpu benches out the same as the Exynos at 1.2 GHz, so while not as efficient per clock, it's plenty efficient to get the job done. I think there may be an edge to the media processing on the OMAP4 - but for practical benefit, all I can say is that the S3 can support _real_ 3D just fine, so it's not like a total dog.
I posted earlier that I had battery concerns on the Rezound, but your experience matches my phone if scaled. I was getting 18 hrs/50% battery at 1.2 GHz, light/moderate use, and easily go a full day with room to spare running moderate/heavy at 1.5 GHz -but with a smaller screen.
What really impresses me is that evidently Verizon's config of the Rezound did NOT end up borking it. I've been a broken record that what Verizon HTC users see and experience is not necessarily shared by the rest of us.
I'll be interested in your feedback after you've owned the Rezound for a while and then get to check it side by side with the Gnex!