Very thanks for your answers.
Ok, here is my final question for the PC:

please have a look at this graphic card list:
https://www.nvidia.de/object/IO_11761_de.html

Wich of these cards would you prefer? (Just have a lokk up to the ultra-high-end cards. The"HDSDI" are to expensive)

I also would like you to pay a special attention to the "NVIDIA Quadro FX 4500 X2" -card because it has special skills for Maya. This is the cart I would prefer. But I´m not a hardware speciallist; so my decision is just "instinctive". And because of that I would be very happy for some replies.
Thanks