our E34 530i (non-sport V8)had very heavy steering - felt like no power steering at all...
the E39 528i (sport package)had lighter steering than E34 but heavier than 4.6iS
the E53 4.6iS was light
the E53 4.8iS is much heavier than 4.6 and a bit heavier than E39 but not as heavy as E34
the E90 335i (M package) feels like there are little elfs fighting against the steering effort - super heavy

never tried an E70... sorry