The x62 is the best one of the models you mention. The H115i is the same pump, block, and radiator, but it has worse fans.
Regardless, the Fractal Design Celsius S24 outperforms them all with noticeably less noise. It has a warranty to match as well. See:http://www.tomshardware.com/reviews/fractal-design-celsius-s24-cooler,5058.html
If you really want an expandable loop, consider the H240 X2 Prestige as well. Just be aware that you'll probably end up replacing everything on it except the fans if you want performance comparable to the S24.