Reading your posts again, it's probably also worth pointing out that what you and I might be considering as "watercooling" may be differing slightly.
There are two approaches to watercooling:
1) Custom loop. This method involves buying all of the individual components of a loop (blocks, pumps, reservoirs, radiators, tubing, fittings, etc). You decide exactly what you want to (and don't want to) cool using water blocks (such as CPU, GPU, Motherboard/Chipset, even RAM), and buy the blocks to suit your components. You then choose your tubing and fittings (flexible tubing can either be compression or barbed, and hardline tubing is typically some form of compression fitting, but different to flexible compression fittings). You can arrange the loop in whichever way best suits the layout of your case (it matters not if you for example go CPU > Radiator > GPU > Radiator, or CPU > GPU > Radiator > Radiator, as the water will reach an equilibrium temperature in the loop regardless). The pros of going "Custom" are that it typically looks far nicer than an AIO, and because you can choose how much radiator "real estate" to put in, you are likely going to get away with slower (but a higher count of) fans, making the machine quieter. My H440 has 2 360mm radiators (so 720mm of radiator "area", 6 120mm fans to cover the space). The cons are cost, and time taken to install.
2) AIO. The "All in One" method has been around for a good few years now and is essentially a sealed simple loop, typically with a pump directly mounted onto the CPU block (as a single unit), and a single or dual radiator either using 120 or 140 mm fans (so anywhere from 120mm to 280mm of radiator "area", using between 1x120mm fan to 2x140mm fans), the radiator will usually also have a small expansion tank acting as a reservoir, though as said, this isn't a necessity. These are usually very simple to install, but far less flexible, and not usually upgradable (the EK Predator being an exception here, using it's quick disconnects you can add more components to the loop). Pros are as said, simplicity, and cost. Cons are flexibility, upgradability and that they are going to be louder than a well thought out custom loop.
Both options above also have the option to double-up on the fans use by installing in "push/pull" (so a fan on each side of the radiator - a 120mm radiator would have 2x120mm fans, a 280mm radiator would have 4x140mm fans, etc), however in testing with many AIOs and custom loops, I tend to find that you get diminishing returns in cooling performance, but more noise. Certainly with a custom loop (case layout dependent) you'd be better off with more physical radiators than you would trying to improve airflow over them.
