The thing to keep in mind about adjusting the preload is that you can't add compression travel without sacrificing rebound travel and vice/versa. More compression travel can be nice, so the damper can compress effectively, but if there isn't much rebound travel the rear end can still react in a way that is difficult to deal with after the compression stroke is done.
What's your preferred ratio of compression and rebound travel? 50/50?
How much preload would you run with 10k springs?