If you’re shooting short subs, it won’t matter because the rates are very close, and aligning the subs will compensate for differences due to refraction.?

If you’re shooting long subs, you should be auto guiding, so it won’t matter which you use for the base tracking rate. ?

If you’re using a 492 digital drive, its King rate is just an average refraction compensation, not particularly accurate for most positions. ?King rate should be marginally better, but really you want to either shoot short subs or auto guide. ?Or both. ?

I don’t know if the Gemini implements position-dependent King rate; if so, it would in principle be better for unguided imaging with subs on the order of a minute or longer. ?In any case, if the mount is properly set up, King rate shouldn’t be any worse than sidereal for objects outside the solar system. ?