Thanks for the spring rate calculator. That will be very useful in the future. Like you, I found the stock shocks to be very harsh even with reduced preload. Lacking that tool I bought Racetech shocks for my '13 V7 in hopes of making the rear more compliant. It took multiple tries to get the RT shocks to work. There were problems with the shock body hitting my rear rack and their initial settings were still too harsh. We finally found a reasonable combination of spring and valving, then mounted the shocks upside down for more clearance. The end result was pretty good. Lesson learned was next time I would go directly to a RT certified shop, someone who specializes in suspension. I found that I was actually going through a middleman and my problems were not being translated correctly to the RT tech. When I finally talked directly to the tech I was able to get some satisfaction. The final setup is (per the RT invoice): Spring 2.2, Spring preload 8mm, rebound adjuster 40 clicks out.
I'm afraid you are going to find that even if you get the correct spring rate you will be stuck with a poorly valved shock body. The stiff springs mask the poor dampening qualities of the OEM shock. If you could pull the shock apart and improve the valving you would have the key to improving the suspension for all of us.