Factory springs are so long your minimum spring preload is 17mm.  This is not good as it creates harshness in smaller bumps, and washboard terrain no matter what spring rate or valving you have. Suspension101's custom springs are shorter, reducing how much the fork springs are squeezed before you hit a bump, making for a more comfortable ride and better performance.
RATES:
The .64kg's are for full plush and smelling roses, very relaxing as long as you are not launching the bike aggressively they are good. 
 
The .66kg's are quite a good all around spring set. Less fork dive, still noticeably more plush than stock and can get a bit more aggresive. This is our most popular spring rate.
 
.68kg's are again still plusher than stock but now you can show your buddy a wheel on his R model. Again less brake dive and you can more readily jump those water bars with less drama.
 
.70kg's are either for an even more aggressive expert rider in the 180lb to 210lb range or a medium aggressive rider in the 220lb to 240lb range without gear.  Believe it or not the reduced preload is so important that even these springs with 6mm of preload will be plusher than stock, but throw down aggressively you can.
All of these springs alone without your oem spacers will net you 4mm of preload. (full Plush).
Quite light and will sink lower when you sit on the bike.
We generally go 6mm to 10mm of preload on the big bikes.
They still sink a bit but it is a good all around setting in this weight range.
With a Gobbler Pro build with any of these springs will pick up your pace 10mph with more comfort, more control, and more Safety. Simply butter!