The KDX is designed as a 1st & 2nd gear bike. Were you to discover 4th, 5th, 6th gear -- you'd most likely need to change to heavier springs. Then, when you got back on the slow tight trails it would be too stiff. Soft springs allow the suspension to float through the obstacles instead of bouncing off of them. A too soft front becomes a real problem on steep downhills even at slow speeds. Weight transfers forwards, the front drops even lower, the steering angle increases and it wants to tuck under. I'd stick with stock for now.