Turntables run at very low speed, but fairly high point loading, so gear oils may be a good choice if advised by the bearing manufacturer.
However - most EP ('exteme-pressure') Gear oils contain a lot of sulphur, because it is a very good additive for high point/shear-loading oils (=the really smelly ones!) These additives also progressively attack brass /copper compounds as used in some gearbox synromesh clutches and turntable bearings....
Synopsis: stay with GL4 oils at most, and do not use GL5-rated gear oils in anything using a brass bearing.