I've had the chance to play with the power supply a bit and found my answer to the output current capability vs output voltage. The current limit that you can set is automatically constrained by the output voltage that you select. E.G. if you have an output current selected and you attempt to set the output voltage to a value that would exceed the 50W max output power capability then the current is automatically reduced to maintain 50W. The converse is not true, if you have the output voltage set and try to set the current beyond 50W then it just won't change the current. And it will also not accept a current setting above 3.75A or a voltage below 0.3V. So, the spec that shows 4A max current is incorrect.
It turns out that the document in error is the Technical Data Sheet: http://www.farnell.com/datasheets/2718447.pdf
The spec sheet in the Operating Manual is correct for the max current but it does have other issues: http://www.farnell.com/datasheets/2720952.pdf
Here's basically what the output range looks like:
Of course, these are just the programmed values. I've verified the operation of the current limit at a few points with resistor loads. I'll start taking some quantitative data once I've gone through all the functionality checks - probably in the second half of the roadtest.