I have an SG03 and it can be very quiet. What I would be wary of is HDD vibration. I soft mounted but still HDD noise dominates my system. Cooling wise it's amazing for the graphics card, not so amazing but workable for the CPU. I use a Scythe Zipand arranged without a fan so it really just atkes airflow from the front to cool it. This could be resolved very well with some ducting no doubt.
I'm a little surprised... The two 120 mm intake fans are a good start, but with no exhaust fans at all, I would have though that restricts airflow by quite a bit.
Also I'm looking at running a i5-3570 and a GTX 660 Ti. Maybe less heat load from the CPU, but I'd think quite a lot more from the GPU as compared to the system in your sig. That worries me.
You could go Mini ITX with a Silverstone SG08, for example.
Or a Lian Li Q08, Q11 or Q18. They have the same "PSU above the CPU"-issue that the SG03 has. I had the SG04 and didn't like that setup very much.
The best Micro-ATX case is Silverstone's TJ08-E. (though I preferred the predecessor without the -E)
Second best would be the Antec NSK-3480, if that's still available to buy.
I do like the SG-07 and 08, but a mini-ITX system is unworkable for me. I do sorta need a spare expansion slot, and the local prices for a decent mITX motherboard are a bit higher than bigger form factors. That would go on top of a new case that I didn't originally budget for.
Was reading the SPCR review on the TJ08-E. Interesting. Are there any alternatives to the 180 mm intake fan? And does having the GFX card on top have an impact on thermals?
I've been looking around at what's available locally, and to give you an idea of prices in local currency:
Fractal Core 1000 - $55
Corsair Carbide 200R ~$80 (I think...)
Fractal Arc & Define mini - $129
Silverstone TJ08-E - $155
Silverstone SG-03 - $165
Antec Solo II - $165
Antec P280 - $199
I think I've heard the NSK-3480 might still be available, but it's more expensive than the P280...
How are the Fractal Arc and Define Mini for a silent PC? Looking at the pictures on the Fractal website, the appear to be basically the same case, differing only in the front and top plates. Trouble is they're as deep as my current Solo (if not deeper!), and almost as tall...