> would a PPC64LE QBox be more useful? G5s should be able to run that

Thanks to its POWER4 heritage, the G5/PPC970 got stripped of any little-endian support the G4/e600/MPC74xx and predecessors offered.

https://lists.ozlabs.org/pipermail/linuxppc-dev/2010-June/082797.html

> no idea about X5000/Mirari.

The e5500 core can be run in little-endian mode (not sure whether true mode or just address swizzling), the e6500 cores on a future T2081-equipped Mirari as well but would have to do without VMX/AltiVec at that.