I'm running option 2 - the ride is a vast improvement over the stock Ranchos. The only time you will increase preload is if the shock absorber is topped out and cannot extend any further, thus limiting the distance between the top plate and the perch. This doesn't appear to be the case on the Z71, at least its not apparent to me.
If there is still room for the shock to extend with the perch used, the overall length of the whole assembly will simply increase instead of adding to the preload of the shock, thus leaving the weight of the vehicle as the only source of preload.
It is like the difference between the two types of spacer lifts. a coil spacer will usually achieve the top out of the shock and so preload the coil. A top plate spacer does not preload the coil, but merely extends the length of the strut. The 5100's simply do this at the other end of the strut.
That being said, if you use a long enough coil with the 5100's to achieve top out of the shock on the perch you are using, you will begin to preload the coil and that preload will increase with every perch you move up.