ProDigit80 - 15m*40W=12m*50W so they are equal so no advantage power-wise for the atom with your example. It takes longer to do the same thing with the atom and the power savings just doesn't justify it.
You are not going to use the atom as a workhorse true, but the fact is that the atom is slow and most of the time it will be used at high load even doing simple things and as I already demonstrated, the atom (platform) is inefficient power/performance.
The problem is not with the atom, the CPU has excellent power/performance ratio, but with the chipset witch uses lots of power. The rest of the CPUs tested have worse power/performance ratio but are performing better and the chipset power use is about the same. The power used by the chipset dilutes the power/performance of the atom processor and that is a shame.
I know some of you will likely contradict me on the power saving issue (estimating power usage on different scenarios) , but really it doesn't matter if I'm right or wrong, it's a desktop and it's only a few W, it won't change the global warming.
I consider the atom CPU a great product, but not for desktop use.
Other (bad) things to consider about the platform:
The CPU is week. Users expect the same level of performance from a ITX as a midrange computer, after all it is a desktop. Already there are ITX boards that use regular desktop CPUs and there are no thermal issues with a small from factor. People buying SFF are interested in design, performance, features not necessary power savings, and as already demonstrated, the atom desktop platform isn't delivering those power savings.
The price needs to be low. Lower then the current ITX platforms since the atom doesn't perform as well. To keep the prices down the platform will use the cheapest chipset/chips available. That's why we have a chipset that uses so much power. It doesn't have a modified mobile chipset or any power efficient chips. All of those cost extra money and will make the atom platform more expensive than the current ITX lineup.
In the end I don't think the users will go for that. Atom for desktop needs to be more powerful and already Intel is working on a dual core version and probably will increase it's speed also.
If Intel pushes atom to a level of performance that the users will be comfortable with, the platform can change the market the same way ultra portables did. Intel might even design a cheap power efficient chipset so the whole platform to be power/performance and price/performance efficient. Imagine a 200$ sexy SFF ... might convince many to abandon the uglier, noisier cousin.
Intel is going in the right direction, but it has a long road ahead and the competition isn't staying idle.
AMD has great chipsets and VIA has power efficient CPUs.
Sorry for the long post