1) 520d is too new, better let the 320d boys answer. the X5 3.0d has also been around a long time, i dont hear anything bad about those cars.
2) 520d engine is 4 cylinder, it actually uses LESS oil - 5.2 liters, i just did my first service. my 6 cylinder M52 engine in my E39 uses 7 liters.
3) all of these weird rumours came from MS123 diesel standard days, the standard is EURO 2 now. our company's W211 E270 CDI has 298,000+km on it and no major fuel injector issues related to "sulphur clogging".
one of the biggest issue that diesel engines face is that with higher sulphur content, soot production is higher, and some of that gets into the engine oil via exhaust gas blowby in teh combustion chamber. when soot is in the lubricant, the lubricant's qualities degrades. as a countermeasure, last time you had to change oil more frequently.
another problem is soot clogs the DPF, from my understanding our local spec cars do not have DPF. My E270 CDI had DPF, they were removed by the previous owner because always get clogged, because it ran for a very long time on the MS123 fuel.
our 320d and 520d have never seen shitty MS123 diesel as they were introduced after the Euro 2 upgrade.
all of this may have been quite bad when the diesel standards were MS123, but now with Euro 2 sulphur has been cut down alot and soot production is also significantly less.