When you really want to game... but the HP motherboard uses some sort of custom 6pin power connector, not the standard 24pin atx plug, so you could only use a gpu that
Acquired Z400 & xw8400 - which 1 to upgrade + issues - HP Support Community - 7346518
Acquired Z400 & xw8400 - which 1 to upgrade + issues - HP Support Community - 7346518