If fan speeds like this are not your idea of a quiet PC then dropping speeds below these levels can only be done by Fan Xpert, and the Asus motherboard would be the automatic choice.
Is the Gigabyte board not capable of doing this as well via the Easy Tune software?
The bottom line is that going the PWM route would cost money, and the absolute minimum spend at Amazon.com prices would be around $70 USD plus carriage (2 x Noctua Redux NF-P14s PWM, 1 x Noctua Redux NF-P14R PWM, 1 x PWM Y cable). But given the standby issue extending the upgrade budget by this amount would allow the choice of the Gigabyte board and still meet your objective of a computer that is really quiet.
How low could I get in terms of rpm with the D14 and R4 default fans using Voltage (without PWM)?
Or you could use LightDims. As the name suggests they provide a varying level of light reduction (50 to 80%) and cost about $10 USD. I have used them. They work best on flat surfaces where the led is recessed. But as claimed they can reduce LED light output from annoying to barely perceptible.
I would use this but unfortunately in the R4 case this is not possible to due to the ring around the power button and the leveled nature of the second part of the power led as can be seen in this picture: http://www.fractal-design.com/media/794 ... 78204c5680
As to the Asus led problem: Use some macgyver duct tape and cover this led.
No need to disconnect the led and risk losing warranty. Just cover it up. Mainboard-makeup
I meant to disconnect the power led cable going from the case to the motherboard.