FWIW I'm using a i5-650 I bought for $120 at Microcenters.
I can stably overclock it to 4.5Ghz (I did so for 24hrs), but since low power is my goal I have it top at 4Ghz - this make <1W diff at idle. With an GB H57M..USB3 bd two sata disks, dvd & 4GB dram, 2 fans it idles at 50-51 watts. I think the Asus offering may be slightly better.
Things to consider -
A/ Among the Clarksdales the features on the chips vary. For example the i5-661 lacks TXT(Intel trusted execution) and lacks Directed I/O (VT-d) which is very important for high performance virtualization. Read the Intel site carefully before selecting.
B/ the i5-661 has a slightly faster GPU (23% faster), and has a 14W higher TPD. I think that's a bad performance/power trade-off. A 23% boost in that GPU is like putting a turbocharger in a Yaris. A faster mediocre GPU.
C/ You can overclock the H*** out of the clarksdales. So I wouldn't worry much about the nominal clock rate. My (nominal 3.2Ghz) i5-650 has been clocked at 5Ghz for a benchmark. The GPU locks up, but the CPU works fine. Olny at 5.2Ghz it chokes.
D/ Sadly for AMD that have nothing with both good performance and low power consumption. Power implies more fans & noise and heat and a basically unpleasant PC.
So yes AMD is marginally cheaper in purchase price. You'll lose that savings to the power company over the life of the machine. AMD certainly wins some specific benchmarks solidly over intel. Read the AandNtech comparisons. If you do loads of vid encoding the AMD is a solid choice. If you can really use 4 CPUs and need this at high performance then choose AMD (the Intel comp is way too expensive).