I think Conroe will be a better bet for overclocking, if you can find a motherboard designed to take a Conroe XE, it should support a 1333mhz FSB.
So if you can convince a motherboard that a 2.4Ghz Conroe is actually an XE, you'll be sitting at 3ghz, and the processor will be a lot less bandwidth starved than a meron. A 2.66Ghz Conroe would be 3.32Ghz by 1333FSB, which is what the XE should be at stock.
I've always prefered chips with the lowest mulitpliers, as they allow for much higher FSB, and memory subsystem performance before the processor maxes out. Only downside is needing to buy the best of the best memory. However dual channel DDR 667 is fast enough to fully saturate a 1333FSB.
Intel should be releasing the 2.9Ghz Conroes by Xmas, and hopefully they will be speed binning by then, if so then 3ghz should be a feasible 'standard air' overclock. (Crosses fingers)