Just wanted to assure you that the xperia m will be vastly superior in power consumption as well as performance per core. The cpu on the xperia m is built on a smaller fabrication process and should be more power efficient. Also a simple overclock to about 1.2~1.3 will close the gap against the htc. The a5 on the htc is inferior to the cpu on the Xperia. Also, In terms of developer support for custom roms and such i would go for xperia.
Yep, I figured as much, the phone will be at my doorstep Tuesday.