>For comparison, the original Xbox used an x86 of the same clock speed

which is fairly useless as a point of comparison, as not only is it the completely different arm architecture, but it is also Arm V6 (arm11), whereas even our smartphones have been arm v7 (cortex A8, A9, A15) for the last couple of years. If i had to equate it to an x86 clock speed, i'd say 400mhz was possibly a fraction generous.