The SoC on the 9 is a samsung design and made in a samsung fab whereas the 10 is more a google design made at TSMC. TSMC is generally known for better quality silicon that runs with less power and making less heat.
Its important to note however, that the MODEM chip is still the same samsung on the 10 as on the 9.
I can't say for certain if these characteristics carry into the 10, but its something that a lot of us have been waiting a long time for. We won't really know how they compare until after GOS finalizes support for the 10. Its very hard to judge based on the factory system because of weird showoffy crap that they do in order to try to make the new model stand out from the old.