Moving back to the older era of 32-bit-only CPUs is the Lenovo ThinkPad T60 with an Intel Core Duo T2300 and ATI Radeon Mobility X1400 discrete graphics. The Ubuntu Linux testing went back as far as Ubuntu 8.04.4 LTS.
When idling the even for this old ThinkPad notebook the power consumption had dropped compared to Ubuntu 11.10 (22.9 vs. 21.9 Watts average), but it is still much higher than Ubuntu 8.04 and Ubuntu 10.04 at 17.5 and 20.3 Watts, respectively. Part of the Ubuntu 8.04.4 LTS difference is due to backlight oddities, but still Ubuntu 12.04 is not quite back to its original levels when this hardware was considered fresh.
The ThinkPad T60 with the R500-era Mobility Radeon X1400 graphics were at their open-source best in Ubuntu 12.04 LTS, but this comes at a cost of slightly higher power usage. In fact, Ubuntu 12.04 LTS with the open-source R500 graphics support was at its highest level of any release tested. While the open-source Radeon OpenGL performance was worse in the Ubuntu 10.04 days, the power consumption since that point is up by 30% since two years ago.