I am planning a uATX- or ITX-sized build with fairly powerful CPU but still low noise levels. I would love to hear your thoughts on my options!

Components:

* Ivy Bridge i5 3570K (77W TDP)
* Suitable mobo, no strong preference here
* 2 sticks of RAM
* No discrete graphics card
* 1x2.5" SDD and 1-2x3.5" HDD
* Slim Optical drive (can be skipped if there is big advantage)

Ideas:

1) Temjin TJ08-E
+ Plenty of space
+ Can be made very quiet
- Needlessly large for my needs

2) Sugo SG05, possibly with 150W PicoPSU
+ Small footprint
+ Should hold all I need, with the possible exception of 2nd 3.5" HDD
- Would fan(s) need to run too fast to reach low noise levels?

3) Other small cases?

When going for a PicoPSU in the SG05, what options for larger HSF combos would that open up? Would this allow noise levels approaching that of a good TJ08-E build or is the confined space still a problem?

Ideas on other small-footprint-solutions capable of housing a 3570K with low noise levels? Given that I plan to not use a dedicated graphics card?

If you're going for the SG05 w/ picoPSU, then I'd get a Scythe Samurai ZZ for the CPU cooler.

I've just ordered one for my build (migrating from a P182 to an SG07). Its dimensions are pretty much perfect for any mini-ITX motherboard. In 3/4 directions it basically skirts just around the LGA1155 mounting holes, thus clearing the PCI-e and RAM slots when the CPU socket is squished right up against both. And then you just need to choose which direction the fin mass goes. It can either go parallel to the RAM slots, or towards the back of the case just slightly over the rear I/O ports. If necessary, you can bend the heatpipes slightly to allow the fin mass to clear any obstacles.

I might be wrong on some of these things though, gotta wait for the parts to arrive first. But I'm basing my comments on many hours spent over the past week comparing photos and putting a ruler up to my monitor to judge the dimensions.

Do you intend to overclock?

That would depend on the cooling performance reached. If there is room for OC without more noise - sure. But I could also consider undervolting and/or underclocking, if that is needed to get a reasonable quiet setup.

Noise level would come before performance, to put it in another perspective.

Other small cases include the Cooler Master Elite 120 Advanced, Bitfenix Prodigy and Fractal Design Node 304.

If you like the design of the Bitfenix, and you don't think it's too big, then it would be a great choice since it's compatible with big tower CPU coolers. And there's plenty of ventilation and fan options which means that even a little airflow will suffice. It also has a 120 mm rear fan. So the tower CPU cooler will have the CPU fan pushing air through while the rear fan pulls the air away from the cooler, out of the case. Great for keeping CPU temperatures low!

Lian Li Q07 fits the biggest heatsink (Thermalright HR-02) with a Pico PSU.
Lian Li Q11, too, which is easier to work with for two 3.5" drives. Q11 fits two 3.5" plus two 2.5" plus full size optical.
Non-oc is borderline passive coolable with HR-02 or similar. a very low <500RPM fan should suffice.