I don't what you're thinking, but a Mac with a PPC chip has far superior battery life than an Intel based chip. For instance, I have an Inspiron 8100 with 850mhz CPU and an iBook with an 800mhz G4. Inspiron lasts maybe 2 hours while the iBook lasts 7 hours. And the iBook is half weight of the Inspiron. Now who's superior?
I don't know - perhaps if you bought an x86 laptop from this century, you'd find the comparison a bit more apt ;)
Seriously, I have a P-M laptop running at 2 GHZ that'll run rings around that dual G4, and get six hours on the battery in the process - a single core P-M, to boot. This should hardly be a surprise - how old is the G4? Anyway, the comment about the cinderblock and the heatshield was a reference to the fact that the "superior" G5 simply doesn't exist in a laptop, and never will. Hence, if you want a powerful laptop, PPC is decidedly inferior. Just ask Steve Jobs.