One other thing that V5R4M5 brings to the table, if you get a slightly
newer system (but not too new) V5R4M5 will allow you to do an
unload/reload to that machine and they upgrade the OS. For example, I
upgraded a 270 from V5R4M0 to V5R4M5 and then did an unload/reload to a
Power 6. Then I upgraded that to 6.1 (and later, on and on...).