When book reading with display@max battery use showy Display using 89% power and GPU overclock is still much less power hungry than CPU one
To test simply use battery monitor widget and brightness profiles program to observe how setting certain brightness profiles influence power consumption.
For me reading a book in Cool Reader with brightness@100% uses around 350mA while brightness@10% uses around 120mA (cpu in both cases @192-1720 but it mostly stays @192-384), gaming @100% results in around 800mA and @10% in around 550mA - these are demanding 3D games
At all that time WiFi and GPS were turned on although not actively used.
CPU is undervolted by -50mV GPU320 version.