Let me state this clearly, I have no formal testing facilities for heatsinks. Whilst my colleague (and usual heatsink reviewer) Mike "Darthtanion" Wright has a climate-controlled environment to test in, I don't have that luxury. Ambient room temperature is a constant 30 degrees Celsius (or very close to).
Idle temperatures were taken by switching on my system and leaving it run for 30 minutes with nothing processing in the background. Load temperatures were taken by letting United Devices' "Think" cancer research program run for 30 minutes. Temperatures were taken according to the Shuttle AV40R's onboard sensor, which makes contact with the base of the CPU. Arctic Silver II was used as the thermal interface for all heatsinks to ensure a level playing field. Just for comparison's sake, I threw in the default Intel heatsink and fan.
Processor: 1.7GHz Intel Pentium 4 processor
Motherboard: Shuttle AV40R VIA P4X266 motherboard
Memory: 256MB Apacer PC-2100 CAS-2 DDR SDRAM
Hard Drive: 15.3GB Western Digital 7200RPM Hard Drive; 2 x 6.4GB Quantum 5400RPM Hard Drives in RAID-0
Video Card: 32MB Prolink Pixelview GeForce2 MX
Sound Card: Creative SoundBlaster Live!
Case: 6x 80mm case fans in an AOpen H600A Midi-Tower case
Result - Idle
The GlobalWin WBW76 is clearly the leader here, coming in 3 degrees cooler than the Intel reference HSF. The Evercool unit doesn't perform too badly, just beating the Intel sink by 1 degree.
Results - Load
This really sorts out the men from the boys. A 1.7GHz "Willamette" Pentium 4 emits around 82 watts of heat under full load, besting even the "Thunderbird" Athlon. The WBW76 is once again the leader, with the NW6-610 coming in second.