Well, my old computer:
Pentium 4 3.0 ghz
2gb memory
Ati Radeon HD 4570
Windows XP
I was able to play with everything set to ultra (except shadow) (I used to play at 25-30 which was perfect to me) EXCEPT that damn Ultraxion. My FPS would instantly drop to 1 at that boss (LFR version, didn't try 10men).
I bought a new one 3 months ago.