PSU fan only connectors and possible overloading

Anotherway to think of it is the amount of fan current equates to air throught the box and the current is limited by the PSU. dosent matter how you share things. So just hook up three and forget it. Actually 4 will run quieter, and you should get near the same airflow. It wont hurt the fans at all. Is the slot fan using bus current? if so, not good.

The PSU is only monitoring watts used. It has no idea of how good the case is at getting rid of those watts and hence has no idea of how hot components are getting. It also has no idea of the ambient temperature or what measures you have taken to cool particular components.

Far better is to control your fans using temperature monitoring.

Ideally, one in the hard disks bay, controlling fans cooling these. I have this and I can hear when very large file transfers are taking place..

Graphics cards seem less sensitive to use and more to ambient conditions and the degree of over-clocking set. Thus manual adjustment once in a while using a temperature display on the front panel is fine.

Although keeping the contents as cool and as constant in temperature is the ideal - this has to be balanced by the noise levels. Most of my fans are temperature controlled and so the machine is very quiet a lot of the time.. but when it maxes out it starts sounding like Concorde...each hard disk has 4 (small) fans..overkill I know, but I have yet to have a hard drive stop working on one of /my/ systems.