Rating the Farm Systems: Preliminary Steps

I've updated all the Top 20 lists, and you can find the menu with links to all of them over on the left side of the page. Teams with major changes I will repost and re-open the comment threads today and tomorrow.

The next step is to rank the farm systems. Some readers in the Fanpost section have taken the grades and, using a variety of different methodologies, come up with a ranking system. Each poster has used a slightly different approach.
Anyone who has done that or wants to do that, feel free to go ahead and continue. You can use the grades as they are currently listed. I have my own ranking system but I'm interested in seeing how the results compare to what you guys come up with. The main caveat: don't count Yu Darvish as a "prospect" for the Rangers. I'm still trying to figure out what to do about him.