So is the Mali 400 like an SGX543MP4 where it actually has 4 graphics cores working in tandem ... or is it just one core separated into four units to handle different types of graphics handling (shaders, tesellation etc etc).

I would prefer the first method, although it is less power efficient, you will see the performance increase instantly. And since things are already quite power efficient (durr ARM) I think that point is less important.
Whereas the latter may require a specific optimization on the software end to take advantage of its unique architecture ... (and you know how often things are done properly these days).