OK, here's the deal: Seriously
Too many people are calling these things by too many different names! Many enthusiast are calling the P4 2.4/400 a 2.4A, while they refer to the 2.4/533 as the 2.4B. Of course, Intel doesn't do that. So what you're left with is the fact that many people call the A a B if it's "533" bus, but that Intel won't be calling it a "B" until it's an 800 bus. Confused?
All P4 3.06 CPU's are 533 bus. There is no 3.00GHz/400 bus CPU. So all these guys are selling the same thing.
If you can get a retail CPU for $20 more than an OEM CPU, you'd be a lot better off, as OEM CPU's come with no WARRANTY. The included heatsink is another reason to go Retail.
<font color=blue>Watts mean squat if you don't have quality!</font color=blue>