The primary difference between the two coolers is the size and shape of their radiators; the H80 and H100 use the same cooler plate and mounting system.
The H80 has a 120mm radiator that'll mount to any system with an appropriately sized exhaust port in the back of the case. It's designed to be used with up to two fans in a push/pull configuration and pushes between 46-92 CFM depending on fan speed.
Corsair H80 and H100 Copper Cold Plate
The copper cooling plate attaches via four screws and supports LGA1156, LGA1366, and LGA2011 as well as all current AMD sockets. There's a pre-spread layer of thermal paste (which we used). The pump must be oriented in such a way as to ensure that the tubes have proper clearance, which typically means they should point towards either the RAM or the back of the case.
Installation and Setup:
We had no problem installing either cooler, though the LGA2011 mounting screws are a tight fit for the cooler head. Considering how much these kits cost, the included instructions are bare-boned. There's a picture guide without any sort of accompanying text and no user manual, product sheets, or included software. This last, we should note, applies to all of the liquid coolers we've seen recently with the sole exception of AMD's FX LC (not included here for obvious reasons). That kit shipped with fan controller software, while everything else is dependent on physical switches or BIOS controls.
Corsair will sell you a fan control kit...for a cool $100.