^ Yeah there is a lot of factors that you gain but I was talking about sway bars and bushings the works not just springs anyways. on the octane I think the only time you ever switch is when you do a frankenmotor for the high conpression build other then that, its all about trying to make the engine happy and knock free, to less will cause knock and to much will cause it, its just trying to find that midium but its hard to do unlees you have maps or some sort of knock telling device.
Its kinda explained here a little migt apply a little to us cause its more 2005+ but its still almost a 2.5 motor
http://legacygt.com/forums/showthread.php/octanei-191569p2.html