trickydickym
The easy way to check is to put a zip tie round one fork leg,not too tight and cut of the tang,and push it to the seal.With the front wheel off the ground place a felt pen mark at whatever the manual says is your wheel travel,measure from the dust seal.160mm I think but check! Put the damping adjusters to std.
Then go for a ride as you usually do but try to get a couple of hard stops in BE careful.
If your spring and preload is perfect(doubtful) the zip tie will be about 10mm from the mark.
On my 650 the spring was OK for me at 95 kilos at 65 you may find the zip tie is nowhere near the mark indicating the spring is too hard.