You don't even have to choose just one cpu type any more. The
HTC Shift, has both an Intel x86 processor running Vista and a Qualcomm processor running Windows Mobile. The latter being much less power hungry. I'm not sure which mode I would use for e-book reading (assuming I would shell out $1,500 for one), since the WM screen is 640x480, vs Vista's 800x480. Probably the longer battery life would win out.