@superxero044 - the back/top is all 140mm/120mm compatible. Lots of people choose 120mm due to more availability of options I guess? I am kind of a gentletyphoon fanboy so I stuck with 120mm.
I recently got the 650D as well. For the OP - I would recommend 2x120mm for the top, and then 2x120mm if you go with H50/H70 as well. I haven't looked into replacing the front 200mm yet, however if you have the HDD bays in the front you are limited to 200x20/25mm.
The GentleTyphoons are a bit pricey, but move a lot of air and stay very quiet on higher RPMs.
I just run ap-13's as the top exhaust fans, and ap-15s on my H70. The case also has great wire management and the airflow. Moving forward to fan controllers and such in a 5.25" bay is my next step, but I have no real need just yet.