Installation:
I will be installing and testing the GELID Tranquillo on the following system:
Testing System:
CPU: Intel Core2Quad Q6600 2.4ghz @ Stock Speeds
Motherboard: Asus P5K-E WIFI-AP
Memory: 4x1gb Patriot Extreme Performance DDR2 800mhz (4-4-4-12)
HDD: Western Digital Green Series 1TB
DVD+/-RW: Pioneer DVD-R212
Video: Asus 8800GT 1GB
Sound: MOTU 8PRE Firewire Audio Interface
Power Supply: Arctic Cooling Fusion 550R
OS: Microsoft Windows 7 Ultimate x64

The Tranquillo installation went without an issue for me. On my socket 775 system I started by removing the old cooler and using some thermal compound cleaner to scrub the CPU clean. After that, it was as simple as screwing the required brackets on the Tranquillo base and then fastening the entire cooler onto the backplate. Clearance was more than adequate for all my components due to the fins being elevated a ways from the base.

Testing:
To test the cooling performance of the Tranquillo cooler I will fresh boot the system and record idle temperatures after it has been sitting for 30 minutes. Load temperatures will then be recorded after 30 minutes of Prime95 blended stress testing. I will average together all four core temperatures to provide an average CPU temperature. Since this is a silent PWM marketed cooler, I will run the fan in PWM mode on the "regular" control setting my motherboard features.

Idle Temperature Avg.: 45.5
Load Temperature Avg.: 54

For maintaining quiet operation, the temperatures I saw from the Tranquillo weren't too bad. Despite being a couple degrees higher than some of the past coolers I have reviewed, it must be taken into account that they were not all advertised as "silent" coolers. If you're going for a silent system, it's a given expectation that you must expect some extra heat here and there. Also keep in mind that cooler performance will vary depending on case size, number of fans, and many other small cooling variables.