Hum, I do have a hack to improve performance but I designed it for mobile android gameplay (I still have to finish and release it); however, those aren't really graphic intensive sections.
Is your MS led indicator blinking a lot while the game lags? If so, your MS may be too fragmented (that also causes choppy videos some times), or maybe you compressed the ISO into a CSO (longer loading times).
You see Type-0 dynamically loads resources (without loading times) in big areas (even if they are not really hardware demanding). If your led indicator blinks while the game lags, it means the MS is not capable of loading that data in time for the game to stay at 30 fps. Try formatting it or defragmenting it. Otherwise I don't know what could be happening, but I'll take a look
~Sky