GUI.

[T-Troll]

David, here are an example of my tool UI, hope it gives you some clues about yours:

I use sensor-based approach:

• each temp sensor can have fans reacting at his value (checked at picture).
• for each fan, user can define reaction curve (temp-boost points in my case, temp-rpm in yours). Number of curve points are unlimited.
• final boost for each fan calculated as a maximum across all sensors it involved into.

I can control power limits for CPU/GPU as well, but it's only available at Alienware (in general).

NB: I use boost values, not RPM, because our gear is really hot, and stopping fans at full load fry it hard. But I plan to play with Passive/Active/Hot/Critical borders later, it's more safe (with limitation, of course).