I would say anyone over 175 needs springs. I'm at 160 and love the setup. When I land a jump, it's like landing on a cloud. If I get too high, it bottoms out so The more you weigh and the higher you jump the more you need stiffer springs. The brake dive is pretty normal considering the 12" or so of travel.

 

My company provides noise and vibration products. I wonder if we are looking at this wrong. When you set up isolation for equipment, you take the total weight and divide it by the mounting points. So, for 1000lbs and four mounting ponts, each spring is rated for 250 lbs -their 25% share of the load. Further, if the center of gravity is offset to one end, the spring rates can be different, but the total would be for the same total.
Say the weight was off center, with 75% one end and 25% the other. That would be 750lbs one end and 250lbs at the other. So this would have two springs rated @ 375lbs ea and two rated @ 125lbs ea.
The weight on the rear of the KLX would have to be more than the weight on the front end, so the rates would be different -but I'm sure that the factory settings are for a light rider.
It would seem that is you took the weight of the KLX full of fluids and added the weight of a rider with helmet and gear and then used the ratio of the stock spring rates, you would come close to the ride loading and then the rest would be taken care of with compression and rebound damping adjustments.