If you need to raise the ISO, Canon EOS 7D has a unique pattern of ISO vs Noise. It is said that:
160 is as clean as to 100
320 is as clean as to 200
640 is as clean as to 400
1250 is as clean as to 800
But avoid ISO 125, 250, 500, 1000 as they present the most noise.. This is because how the sensor use voltage regulator for the sensitivity of the light sensitive elements. The native value for the sensor power start at ISO80.. to make the sensitivity of ISO100 the designer raise not the power but the resistance.. they have to raise the level of resistance again to get ISO125.. thus giving more noise.. but when they want to achieve ISO 160, they just double the power and remove resistance.. resulting in an image with less noise than ISO125.. for ISO 200 they increase resistance 1 notch and for ISO250 they raise the resistance another level.. but at ISO320 they just raise power without resistance.. the balance between double of power and increase of resistance make ISO 160 about the same noise to signal ratio to ISO 100.. and ISO 320 about the same noise to signal ratio to ISO 200..
You can refer to the test result here.. http://marvelsfilm.wordpress.com/2009/10/10/canon-7d-noise-and-iso-test/