yes, you're right. of course it's only 25% wasted, but 33% more.
i have to admit, that i did not have a situation yet, where storing pixels using 8 bits per component makes sense on the PPC - especially considering that RGBX8888 takes twice the memory and bandwidth of RGB565...
i could be useful if lots of blending is used, but then it still takes a lot of performance.
DANIEL