If iMacs can only handle a 55 watt CPU, I think the following Intel CPUs are possible candidates for the new iMac.
They're from the Clarksfield lineup and may be comparable in performance to the top of the line Intel Core 2 Extreme QX 9300, released in 2008.
Intel Core i7 720QM - 4 cores/8 threads @ 1.6 GHz - with TurboBurst to 2.8 GHz - 6MB cache -- TDP 45W - price per 1000 -- $364
Intel Core i7 820QM - 4 cores/8 threads @ 1.73 GHz - with TurboBurst to 3.06 GHz - 8MB cache -- TDP 55W - price per 1000 -- $546
Intel Core i7 920XM - 4 cores/8 threads @ 2.0 GHz - with TurboBurst to 3.2 GHz - 8MB cache -- TDP 55W - price per 1000 -- $1054
The last processor is currently Intel's fastest mobile processor.
From what I can gather given the excess of Intel processors, I guess I would be satisfied with this, though I'd rather they include an i7 860 which outperforms it, but unfortunately has a TDP of 95 W, yet has a significantly lower price of under $300. Who knows what Apple has planned, but I still wish they would just create an aluminum enclosure sized similarly to a PC ATX Mid Tower and name it the Mac Pro Mini. Sure it will eat into the Mac Pro sales, but it will just be a lower tier of components found in the Mac Pro. Oh, and while I'm dreaming, an ATI Radeon HD 5850 or 5870, since the nVidia Fermi won't be available until 2010.
I don't know about the pricing of the processors, though I did find out that Alienware is selling their M15x laptop series with options for each of the above processors, though they appear to be charging a $168 and $260 premium over their presumed cost for the processor upgrades (which Apple will undoubtedly
I know I'm going to be comparing the price of the new iMac with Dell's XPS laptops just to see if the pricing of the new iMac is fair.
In any case, I hope the processor model in the new iMac is clearly spelled out.
My iMac wish list -- i7 860 processor, 4GB RAM, ATI Radeon HD 5850, Blu-Ray, Matte screen option, USB 3.0 (or eSATA)
BTW, an Intel Core i7 860 has 4 cores/8 threads @ 2.80 GHz - with TurboBurst to 3.46 GHz - 8MB cache - TDP 95W - price per 1000 -- $284 (!)
An Intel Core i5 750 has 4 cores/4 threads @ 2.66GHz - with TurboBurst to 3.20 GHz - 8MB cache - TDP 95W - price per 1000 -- $196
One site says that the i7 860 is a better performer than the current Mac Pro's single Xeon W3520 @ 2.66GHz.
Given the higher speed and hyper-threading of the i7 860, it seems that the current and future use of Snow Leopard's Grand Central Dispatch make it a better long term buy than the i5 750, though the performance is fairly close. OpenCL probably will have more of an impact with system performance, though I haven't read much about how this will work out.
I really think with the prices of the i7 820QM & i7 920XM (and their comparison to the above specs of the i7 860) it is all the more reason for Apple to 'Think Different' and reassess the need for a more cost effective 'Mac Pro Mini'.