One thing I forgot to point out about the rear suspension on a linkage bike is that the linkage depending on its geometry can be "progressive" or "linear". In most of my studies almost all linkage bikes have a progressive rear geometry making the force applied to the wheel while riding in the compression direction increase through the suspension travel allowing the suspension to absorb small stuff while not bottoming out when hitting harder terrain.
So purely as a example lets say at full rebound it takes 50lbs to move the shock 10mm, at bike plus rider weight lets say (static condition) 350lbs will move the rear shock 50mm now lets say you got a bit too drunk at the local bar and scored yourself one of them "snow cows" (women in the upper parts of Michigan
) apply a extra 300lbs to the rider plus bike weight it will compress the rear shock let say 35mm. Once the hang over is worn off and you got away from the heffer you can plot your suspension travle based on weight vs MM. this would result in a curve, the curve will illustrate how many lbs to mm of suspension travel based on the position in the travel. knowing this can allow you to change either your spring or shock valving to better suite your needs. Another thing that allot of guys found out is using lowering links on the back of the XRL changes this geometry and from the testimony I have read it appears to allows the rear suspension to not progressively get as firm though its travel vs the stock link.
That sexy KTM 500 that was posted has a very close to linear spring rate due to the force created by the rear wheel is not mechanically increased or decreased by a linkage setup. A old co worker had a older KTM525 (non linkage like that 500) and he was raving how a progressive rear spring really improved his suspension setup.
Just more food for thought