The 2.4A goes to 3.2GHz at 133MHz FSB, which is QDR533. The 2.4B would require 177.7MHz FSB to get to 2.2GHz. The most efficient board (more power per MHz) is the 8SG667, but I don't think that it's chipset will do much over 166MHz bus. That leaves less efficient Intel DDR chipsets and the i850E.
The i850E will definately go 178MHz, but most motherboards don't have clock generators that will. Aopen is the only exception I know of. AX4T II-133 looks like a nice board but I've never seen it in review or in action, so can't cake a recommendation. One thing I do know is that at 178MHz, your RDRAM would run at PC1066 speed using the PC800 multiplier (3x).
Getting back to DDR boards (more bang for the buck, er, slightly less bang for far fewer bucks). The Asus P4PE looks like a great board, it uses the i845PE. The Gigabyte GA-8SG667 looks to be a slightly better performer, but I'm not sure how far it clocks (only seen it verified to 162MHz, but that was at stock voltage).
Almost any board would be fine for overclocking the 2.4A to 3.2GHz, I could even do it on a stock Intel board with a few tricks (see <A HREF="http://www.crashmania.tk" target="_new">http://www.crashmania.tk</A>), because 3.2GHz comes in at Intel's next stock bus speed.
I hear the 2.5A comes with a newer core revision that allows for higher clocks. It should do 3333MHz at 133 on almost any board. And I've heard the 2.53 has similar improvements.
Intel is dropping their prices again soon.
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