I went with the 8kg which is rated for 251-350lbs. I'm about 230lbs so I figured this would handle me, panniers, and gear. Haven't been able to sit on the bike yet to see the difference, but visually compared to the stock spring, it's noticably stouter.Did that job a couple months ago. Needless to say, I won’t be doing that again.
What rate spring did you end up going with?