It's not an option because of the d3d video plugin not supporting it your card should support shader model 2.0 so I switch plugins and use pete's opengl 2.9 you will then have the option to select 512 from the dropdown list also 1.70 does have issues with final fantasy 9 use epsxe version 1.5.2 make sure you have the special game fixes enabled and click ... and select the one that says it's for ff9 and the one that says it needs to be on for epsxe 1.5.2 if you need a link for 1.5.2 here you go
http://www.epsxe.com/download.php
your plugins and bios for 1.7.0 will work with 1.5.2 no need to redownload those.
also after you get used to opengl2.9 you can use custom shaders to make final fantasy 9 look better than original here a screen shot for you to look at