[wejones]

I think I would use the 5.31 even if you can't get to a sat with that declination, because there is still a slight contribution from the motor elevation at sats you can actually see (I know that probably doesn't make sense).
But realistically, it probably doesn't make a whole lot of difference, because both are probably so close to each other that you can't tell the difference, plus you probably can't set or measure the angles that accurately anyway. I think my main goal would be (1) with a big dish, set the declination to less than the south declination by something a bit more than a half degree, or (2) with a small dish, set the motor latitude setting to more than your actual latitude by a bit more than a half degree. Basically, when you set these angles, it's usually not possible to set it to a precision of tenths of a degree, you can usually just get close to the nearest half degree. I see people setting their latitude setting, and rounding off to the low side, but they would be better off rounding off to the high side. As long as you get to within a few tenths of a degree, I don't think you'll be able to see a difference.