Higher rate springs or longer springs?

I have an XP 900 with King 2.5 shocks. I want to raise the rear ride height. What is the correct way to raise the height without impacting the ride?

I was thinking higher rate springs, but I am concerned this will have the same impact as adding more pre-load. I was also thinking taller springs.

I am not very good with suspension stuff. Any help would be appreciated.