'10 Sachs rear shock setup

[Bailey28]

Hey guys, please check this and let me know if the spring rate here is right for my '10 EC300:

The manual says that as delivered the 5.2 spring is preloaded to 258mm.

After a few rides I turned the preload ring in two full turns.

I measured the free sag at 30mm, and the race sag at 110mm. The length of the spring with the two added turns on it is right at 250mm. Bike feels good, handles jumps,, doesn't feel harsh and corners well. I left all of the clickers stock on the shock and fork.

I weigh 185lbs. in street clothing.

I don't think one turn on the preload ring is worth 4mm so maybe the shock was tighter than 258mm as delivered in the crate. I bought it new. Anyone know off the top what one turn of the ring is worth in mm?