The XSPC kits are an excellent (IMO) way to get your start in water cooling. As the RASA RS 120 kit comes I would expect it's performance to be near that of the Corsairs. The RASA is a very good waterblock, only recently being replaced by the Raystorm in XSPC's lineup. The small radiator is the two weak point in that particular XSPC kit. An additional radiator might be one of your first upgrades.
On the other hand, there are the two Corsair all-in-one units which are good enough for most overclocking purposes and are considered to be the equivelent of a high-end air cooler if configured in push/pull (four fans).
I personally have used all-in-ones and I keep one on hand as a back up (for if I lose a pump or something) but much prefer the XSPC (or other) kits