my friend recently bought 1100D, so i could compared it side by side to my 70D.
- there are differences of course.. 70D has much better 19-point AF system including LV focusing, this really counts only with fast motion and sports, viewfinder is much bigger and brighter, body is bigger and has better ergonomy, fast burst rate and bigger buffer, MFA, WIFI,etc... just newest canon tech.
but for the price and in good hands, 1100D is amazing performer, one downside : it has 12mpx sensor, so it is not so cropping friendly as other cameras.
for video and close up boxing, i think 1100D is sufficient for now, invest your money lenses - preferably fast telelenses (70-200 f/2.8)