Finally after long contemplation I finally ordered my Oracle VM lab pc.
this is the configuration
Intel i7-3820 Quad Core Processor (2 threads per Core )
Video Card ATI Radeon HD5450
MotherBoard Gigabyte GA-X79-UD5 (8 dimm slots ==> MAX 64GB)Antec Performance One P-280 Case
changed by fractal design TTXHF3 (that was easier to get)
32 GB of RAM
Extra network card
4 * 1,5 TB Seagate Drives
1 * 500 GB Samsung install drive for oracle vm
Still think if i should get raid adapter or not 
UPDATE 18 MARCH 2012 with actual components
UPDATE 19 MARCH 2012 : probably should get raid adapter as it seems to be only supported way to get raid working under oracle vm …,;( no software raid apparently
