apb3
OS X is likely to work the processor harder than OS9. The reason for this is the extra stability that OS X exhibits. The extra stability is due to multi threading and better managed memory. The OS needs to do more work managing these threads and the memory and so will be more active than OS9. This extra activity uses more processor cycles, and therefore more power. You will find elsewhere on this site discussions as to whether OS X is a UNIX or not. These describe OS X as a micro Kernel operating system, where there are many kernels all working together to run an application. The communication between these micro kernels needs to be controlled by the OS, all taking up more processing power. There is little that we can do about this use of the processor - the slight loss in speed and batter power is more than returned (in my opinion) by the enormous gain in the stabililty of OSX.
Regarding the HDD - I am not sure about partitioning. I presume that a logic partition equates reasonably to the physical positioning of the data on the disk. Otherwise keeping your disk de-fragmented will help.