I suppose that works well because the Probook has no discrete GPU. The Asus has a discrete HD 7730M in addition to the iGPU. Pretty sure the power problem is because both GPUs are active, there's no tool to turn one or the other on or off.
With Catalyst I can use the control center to select one or the other. Even with Catalyst if I just boot into text mode, the temperature rises rapidly; it seems that the GPU configuration doesn't happen until X loads up. Frankly I would have expected the default boot-up mode to leave only one or the other active, regardless of whether X is running.
Thanks for the tip. I uninstalled catalyst again and reinstalled the radeon driver, and reenabled KMS. So I see /sys/kernel/debug/vgaswitcheroo and it appears to work. At boot, both cards are on. Doing an "echo OFF > switch" seems to turn off the discrete card ok. However, after that, lm-sensors reports
Adapter: PCI adapter
while before, it was reporting a plausible temperature.
The CPU is reporting 42C which is an improvement over the 56C it was at before, but still nowhere near as good as the 27C that it shows when using catalyst. powertop reports 26.2W and battery life of 2 hours 7 minutes, so this is still 2x worse than with catalyst.
Also, the screen is still black (no backlight) after a resume from suspend.