Yeap, pwm fans are great, here is the f12 review http://www.xbitlabs.com/articles/coolers/d...oundup-1_2.html
http://www.silentpcreview.com/forums/viewtopic.php?t=60147
yes GT is silent, but its really hard to mount into HSF, especially if your HSF is Thermalright or Noctua, which using the steel clips,
http://www.xbitlabs.com/articles/coolers/d...p_18.html#sect0
plus GT has large fan hub, which it is not a good thing, large fan hub = bigger dead spot on heatsink, unless using fan shroud.
i've tried many fans actually, 1600rpm fan is already enough, high speed fan dont reduce much temps and its loud as hell, especially those are over 2000rpm.

Im using Noctual p12 1600rpm PWM version though, except the ugly color and a little bit pricey, its a great fan actually.

Side fan is important if you are using high performance GPU. though mainstream gpu already can produce a lot of heat, eg GTX 560Ti.
without side panel fans, the heat produced by your GPU will circulating inside the casing and will increase the ambient temp of your casing.

one side fan is already enough, either 1200/1600RPM, or 45 to 60CFM fans.
Case fan most ppl would recommend Arctic F12, cause its cheaper than other fans

Of course is the 200mm fan with 700RPM speed is better, low RPM = low noise, and bigger fan blades = more CFM, but depend of the fan design, bearing ect.
Smaller fan usually need to spin at higher speed to produce same/more CFM than bigger fan.

PWM is controlled by PWM signal pulse, not by voltage, although PWM fan still can be controlled by voltage, if you plug it into 3 pins fan header.
The CPU fan header with four pins will provide PWM signal to control the PWM fan.

Depends on your motherboard, The recent ASUS mobos can control all the fans via software, either voltage and PWM. Gigabyte can do the same but its very limited iirc.