I would have thought that 140mm PWM fans using a splitter from the CPU would have been the best solution. Genuine 140mm size PWM fans are not particularly easy to find currently. In the UK you could consider the Akasa Apache 140mm PWM fan http://www.scan.co.uk/products/140mm-akasa-black-apache-s-flow-blade-design-fan
. These fans can be used with a PWM splitter for two or more fans. Akasa have recently brought out this one http://www.scan.co.uk/products/45cm-akasa-flexa-fp5-pwm-5-fan-splitter-black-braided-cable-powered-via-4-pin-molex
. The splitter draws the power for all fans from the PSU and the control signal only from the motherboard. This should give you a one time 'fit and forget' setup.
The splitter would enable a rear exhaust PWM fan to be included on the PWM fan chain if required.
Whilst motherboard controlled fans are a great idea, one which I've toyed with myself, it is not an absolute requirement. Those fans go on my list of nice choices.
The Corsair fans that come with the H100 sound awful at spin up voltage but can be turned down to turn at a 'silent' level. At that slow level it keeps my i5 under 65C in it's overclocked state which is amazing/acceptable. It's a hassle and what I'd like to do is be able to set my fan controller to one speed and let it go (or motherboard control solution as outlined above).
I think I am able to control the normal (old fashioned now?) 3-pin fans via the motherboard (will have to test that out, quite fiddly) so that might be a route to take.
Is there any conclusive 120mm vs. 140mm fan data out there with the exception of the XBit Labs stuff that just makes me want to buy Scythes (probably Gentle Typhoons with another 120mm Slipstream 1200 exhaust)?