Hoya sp. IV From WMZ is very like Hoya macrophylla in both leaves and flowers.  Hoya polystachya has much larger leaves but the flowers are very similar.  Of the three plants, I would have to say that I prefer polystachya, because of the huge more impressive leaves and the fact that it grows better for me.  Her are two more photos of Hoya sp. IV From WMZ: