Forward current for SMD 5630 LED?
The Samsung spec sheet for their 5630 rates their device (forward current) at 150 mA, but throughout the majority of the document, they use a forward current of 50mA. 


That means that you can run them continuously at 150 mA provided you don't exceed any other limits such as operating temperature. See the Forward Current Derating Curve. Note also the Relative Luminous Flux vs Temperature.

Predicting the operating temperature (of the chips) will be your problem. 


  The "50 mA" number is also referred to as "sorting current," which is a term I'm not familiar with.


The LEDs are graded by colour temperature. You may have to pay extra for this if you need them with tight tolerance for a critical application.



Figure 1. Chromaticity coordinates and diagram.

The left graph shows the position of all the LEDs in the CIE chromaticity diagram. The right graph shows a close-up with the eight grades of "white" that are available. "Sorting" is done by machine and, according to the datasheet, is carried out at 50 mA. Depending on the colour temperature the LEDs are sorted into bins. The table above gives the X-Y coordinates of each grade.


  So, the question: when specing a power supply for a SMD 5630, which number do I use (or perhaps better asked: under which conditions would I use one number over the other)?


You can choose any value up to 150 mA provided there is adequate heat removal.



Figure 2. A colour version of the CIE chromaticity diagram showing various white colour temperatures.