I think what people might be missing here is that deflection is measurable with a scale/rule as in Mark's pictures, but the missing link here is how much force did it take to deflect the belt "X" amount of travel?
Belts are belts and I KNOW these are not Harley's, but Harley uses a belt force weight of 10# to reach their desired amount of belt deflection.
With the proper tensioning gauge everyone would be apples to apples. Without a consistent force at the desired deflection, it's still no better than a SWAG.
There are tons of these available here and in the UK. All have measurement scales so you can see the amount of pounds needed at a specific deflection of the belt.
This is my opinion only, but from what I've seen it's just a shot in the dark without a proper tensioner gauge.
