True, Linux runs best on x86.. the only sellingpoint in Pegasos2 for you is MorphOS.

You seem to be to be pro OS4 judging by the fact that you mentioned you would 100% buy Pegasos2 if OS4 was for it, so in my opinion the only way for you to go are the forthcoming OS4 solutions, PowerVixen or Troika-board. Don't hold your breath while waiting :)