[Forgey (Paula)]

Have a look at this chart, Canon DSLR comparisons for Astro Imaging http://ghonis2.ho8.com/DSLRcomparison.html
And these links compares the 550 and 1100d http://ghonis2.ho8.com/T3iReview/T3iReview.html and http://ghonis2.ho8.com/T3review/T3review.html