Don't know compared to stock cooling, this is a 35w 2400+ XP-M chip I'm using, comes OEM only so the only heatsink to ever touch this thing has been my SLK-900A and vantec tornado which keeps it at 38-39C full load whereas the bigwater was lettin it slip to upwards of 45C full load. Mind you my CPU is OC'd with 1.825Vcore even down at 1.7 vcore the bigwater didn't compare to this particular heatsink and tornado.
You're better off saving up $75 more and building one yourself from danger den. Use a TBX style CPU block, MCP650 pump from swiftech, tygon 1/2" tubing and the heatercore they have available on their site. Mind you a heatercore is different from a radiator..it's thicker and will require two 120x38 fans. That will definitely give you way better results than the bigwater.
EDIT: If anything I'd suggest this kit over the bigwater:
bigger tubing and good block will allow for easy upgrading down the road.