With lowered settings and high resolution, there won't be muc jaggies here and there, so it will perform well, but not as good as running the game in high detail and low resolution.
I've got an 8400GS,
Batman AA runs well at 640 X 480, at high specs ( apart from a few, that are off ).
But, the game doesn't run well for me at 1600X900 ( my native resolution ) and with lowered detail.
Either way, it's best to keep a balance with the settings and resolution, for example, by playing the game on med and at 1024X768 etc.