Photographing Jewelry and dance/movement perfomances in low light.

If you're willing to spend the money on a 70-200mm f/2.8, then there's really no reason to waste time with a consumer grade rebel. The focus a lone on the 7d will give you an advantage in your dance work. For shooting jewelry in a studio, the camera is far less important so long as it meets the minimum needs for output.

If that is all the difference in price, then it's a no brainer what to buy especially considering the vast difference in focusing abilities. That obviously favors the 7D but you really need to phone 1-800-CANON and have a tech person help you to set the "Custom Function" focus page up correctly. When it is, you can photograph literally anything.

I predominantly shoot action sports but do my share of people, nature and other types of 'still' photos.

My friends and competitors keep upgrading to 7D's based upon my recommendation during the past three years. Everyone is glad they upgraded.

Although the f2.8 lenses are great for low light, they also give you a narrow depth of field, which can possibly lead to a marketing problem with your photos.