Till,
Sorry, don't have time to go into everything on this. If I remember correctly, the 150 is a monster with huge current capability and rather "gross" properties, such as the gate capacitance, charge under the gate, etc. This means it's slow and needs a bunch more drive. You use a single 150 in a ZEN, but 6 '240s in an Aleph, for example.
The 240 has high voltage and relatively large current capabilities, and the parasitics that would slow it down are smaller, which means you don't need a honking huge driver stage and it's faster on transients. It is also readily available to US DIY'ers at Digikey - I don't know about foreign shipments on parts like that.
Get yourself the datasheets from the International Rectifier website, and just compare the parameters one by one until you see a transistor that suits your needs. For an Aleph 2, the 240 is your baby.