When a user declares that their system is dead silent with fans running,
I would suggest a hearing problem.
Just between us, I can expect total silence and my systems are ZERO decibel systems.
Of course, my expectations are not typical.
The monitor I am looking at generates an almost undetectable sound that requires I put my ear up to it to hear it. There is a florescent light making noise in the room. I can hear the raindrops, the wind and passing cars outside. My refrigerator makes noise I can hear from another room.
Noise tolerance is personal and varies.
My PC and components have no moving parts unless a keyboard and mouse are considered moving parts.
No optical, SSD only, fanless PSU, passive CPU cooling etc...
As far as performance, an i7-3770k rocks and stays cool as it is a low max TDP cpu (TDP 77 watts).
Overclocking is not an option for typical silent use.
Neither are 3rd party fan cooled GPU's.
One does not normally overclock or need a high performance graphics processor
to do business transactions, email, web, or spreadsheets.
On occasion, I connect an external drive that is safely removed and shut off when done with.
I have not experienced this and have been fanless for years.
Performance and cooling capabilities are scaled on a bell curve as defined by CPU characteristics. An atom cpu passively cooled in a mini ITX box can perform admirably in the proper scenario. A properly heat sinked passively cooled xeon cpu running a server can run for years dust free and within acceptable limits.
It all depends on whether a cpu is properly heat sinked.
Of course, a gamer, or a user that demands a hot cpu a.k.a. > 140 watt TDP < will be well served with an active cooling system. It depends on the definition of performance. An instant on app can happen with an atom cpu. How much processing power that is required to accomplish a task depends on the task. An overclocking extremist is not typical. Neither is GDDR3 / 5 and GB's + of video memory to do normal work. Comparatively, to do video conversions or massive file movements or handle streaming network traffic, fan cooled GPU's depend on CPU capabilities to function accordingly and as such are not always needed to get a high performance grade result.
Heat sinks can be the computer case itself, which is a concept that not many users are aware of.
Passively cooled systems can last for years and remain dust free, and are quite common in industry and server farms that are not typically well suited to fan cooling within server blades although they do exist.
Actively cooled systems are a magnet for dust.
So the concept of severe limitations on performance capabilities falls short if a passively cooled system is properly designed and used in accordance with the capabilities of a given cpu.
A fanless passively cooled system can perform without limitation
and remain silent, clean and dustfree for years.
Quiet PCs and Quiet Computer Parts | End PC Noise