Its weird with Asus, on my Gene Z i also have 60% restriction on Chassis fans, but i seen comments from other people on that they even can control 3pin fans below 60% with Asus AISuite / FanXpert, check **Official** ASUS ROG Maximus IV GENE-Z68 & Z68(Gen3) Owners Club
, check the following posts, post #4204
and post #4156
, there are others, just dont have the time to search, but check the thread.
I did had an Asus P8B WS briefly connected 6 Scythe Kama Flex PWM fans, and all were running at 450rpm or so under idle on Chassis fan connectors, i didnt toy with it too much as i had trouble with the board being stable for my server and return it in couple of days, but what im trying to say is that not all mobos are like Gene Z, or not all Gene Z have the problem with Chassis Fans.... its better to research more about this subject. I think Asus hasn't invested the time because doesn't seem a wide problem for all, but a bios revision without the 60% restriction could easily fix the problem, but then again this is just my guess.
Now i also own 2 intel Sandy bridge mobos, in mini build an H61 and one board that i was using for my server Q67 but change my mind after some issues with WHSv1 (i had a nightmare getting up my sever, but now with supermicro and xeon its alright). Now on both mobos, i have tested with Scythe Kama Flex 120mm PWM Fan (SA1225FDB12H-P)
, and in both mobos i can drop them down to 300rpm on case fan connectors, intel has a restriction of 30% for case fans and 20% for CPU fans, much better imo than Asus 60% policy. What i haven't seen is if he intel mobos will increase the speed as CPU or other component rise in temps, but i have huge heatsinks and the cpu temps stay very low on either case. Now on Asus both Gene Z and P8B WS the CPU temps did increase the PWM fan, i manage to get under WHSv1 for a day, and ran prime 95 on it to test for stability as i had some issues, and the kama Flex did move from 450 to almost 700rpm, this i havent seen with Intel mobos, but different bios, different policies into how the bios manages fans can justify this.
Again this are just my personal experiences, take my comments with a grain of salt, and research more about the mobos you like. Just as comment, most of the MSI mobos that i seen come with only 1 or 2 PWM fans connectors, the rest seems 3pin, weather or not you can control the 3pins (as some mobos can) idk, but just throwing it at you, so you check the mobo layouts also for fan connectors.
Option 1: I mount two of the Scythe 1200 RPM fans (3-pin Scythe SY1225SL12M) and connect them to the Chassis fan on the motherboard. I run some tests and set the speed (down to that 60% limit...which should be plenty low) that best balances thermal and noise using ASUS's Fan Xpert or SpeedFan.
Option 2: Instead of the 3 pin fans, I split the 2nd CPU (PWM) connection and power the two intake fans (Scythe SY1225SL12LM-P). So the CPU 1 will power the CPU fan and rear exhaust while CPU 2 will power the intakes.
Now getting into the options..... i like Option 2, Gene Z can go lower than 60% in bios with the CPU headers, check post #4184
, around 370rpm using Scythe Slipstreams PWM fans (which should be inaudible). So you could just get Akasa Flexa FP5 PWM 5-Way Splitter - Smart Fan Cable (AK-CBFA03-45) $7.95
+ 3x Scythe SLIP-STREAM PWM SY1225SL12LM-P $9.95
, the extension will not overload the mobo header as it draws power directly from the PSU with a 4pin molex, just uses the header for PWM and rpm signal (this is the way i connected my Scythe Kama Flex when i was using the Asus P8B WS as the mobo didnt have enough 4pin PWM headers for 6 fans), you can easily hide the cables on the back of the case.