I've used an Alpha 8045 trimmed a bit to fit on my P4 rig. It is a huge heatsink. The 8942 is even bigger. The performance is greatly dependant on the fan used. It's pin count and thereby it's suface area is greater than even the swiftech478. The pins are hexagonal and densely packed so a high cfm 80mm fan is what to use. I experimented with a Thermaltake adjustable speed fan which would operate at 2700rpm to 5000rpm. I burried the thermister in the pins and stuffed a wad of cotton over the thermister so direct airflow wasn't on the thermister. It would operate at 3000rpm at idle and up to 4000rpm full load. The response time was ineffective and it would never reach full rpm's. I suggest not to use adjustable fans at all on any heatsink. I ended up bypassing the thermister and operating at full 5000rpm for much better results. The noise is still a lot less than my old PIII setup with a delta 60mm fan.
When the comparison reviews on the Alpha come out just keep in mind to check what the performance level of the fan is that they use. It would be easy for unscrupulous reviewers to downplay it by using a POS fan.