The PSX 480p hack is pretty neat if it suits your monitor. I'm using a multisync (240p480p) VGA monitor, so my senses tell me that when I enable a 480p hack, the monitor should render the graphics @ 480p.
This doesn't seem to be the case, I output dual feeds (one VGA and one HDMI) from the MiSTer I/O board, one to my multiformat monitor and one to a 240p/480i monitor. When I switch to '480p mode', I get the message that the hack was enabled when I start a game. The thing is, my 480i monitor is able to sync to this resolution with out any issues.
So unless I'm missing something about the hack, it isn't actually 480p, or maybe it only works for specific games?