Yeah, it sucks they lock the GPU. Maybe a hack will arise to correct this.
As for my G4 iBook, my powermac runs circles around it, but my xbox 1, at several times weaker than a Cell, could render more graphics in Linux because the GPU can be used.
@Paolone
No, sorry it isn't anything like it. I've used AROS and since my first try i have stayed FAR away, its so unpolished. Also, any X86 HW available is nothing close to an Amiga, nowadays, taht belongs to the SAM and G4 macs, since MOS has better compatibility than OS4 or AROS.