Choosing correct spring rates

Hey guys.

Have a yz250 and trying to work out which spring rate to go on the rear.

I am 85kg's/187lbs without gear, c grade motocross rider

currently sag is set at 100mm race sag, 30mm static sag. I know this kind of puts me in the window but I have the preload wound about half way down the thread on the shock.

The confusing thing is I seem to get different rates depending on where I look.

Checking the racetech calculator puts me on a 5.5 rear spring,
A local suspension guy said a 5.4 but that was with his valving of both the fork and the shock,
MXA says go up to a 5.0 if you are fast or fat and at 85kg's I assume I am heavier than what yamaha set the bike up for.
mx tech's spring chart is with gear and puts me on a 5.1
Q Springs chart puts me on a 5.0

Checking my manual the bike came standard with a 4.9 rear spring. I'm kind of tempted to go with a 5.3 and just split the difference.
With all the different recommendations how do you go about getting the right spring?