It seems that running with OPP3 will provide this. Does anyone know how to configure the Gumstix 3503 boards with OPP3? I'm guessing this would be achieved by a #define or parameter to u-boot. I'm currently using U-boot 2010.09.
EDIT: I was able to run clean video through the ISP of a new Earth STORM @ 600 MHz (OMAP 3703) with a pixel clock of 72 MHz. This has not been possible on all 3503 and 3530 boards I have tested using identical mpurate and pixel clock. I have a large number of systems built with 3503 boards, however, and I still need to reproduce this behavior on that platform if possible. I still think the OPP=3 setting could help there, but it isn't clear to me what the default build is booting at. U-boot reports a boot message on the console at startup stating it is at OPP2, but I searched and found that it is hard coded. It isn't clear if it is modified at a later stage based on mpurate or something else, and I can't seem to find any explicit mention of OPP levels in /proc/cpuinfo or the like.