I think RT's formula may be wrong.
This thread has more info. A 160lb guy (though he is a top-notch racer) said it was too soft for him. RT's variation between street and race rates is under 2%, but this was 11% stiffer than RT's suggestion for his weight and he still said it was too soft. With that much difference, I don't think it's just that he's a pro who wants a stiffer suspension than us scrubs.
It's also possible that the NewGen's spring is softer than stated. In my non-scientific experience with that spring/shock on the 500, it doesn't seem to be drastically softer than stated. However, the 500's spring is extremely soft, so it doesn't take much to be an improvement. Based on physical dimensions, the spring seems to match up with the stated rate too.
I would definitely trust your real-world sag numbers over RT's calc, assuming there are no other problems with your suspension causing you to get bad readings. Based on the stated rate and RT's calculator, the stock setup should be quite a bit stiffer than many owners would want. Yet we don't hear a ton about the spring being way off for everyone. I have no trouble accepting that the stock spring is less than you actually need for your weight. But I'm not sure where the error in the calculation is, making it hard to figure out what rate you do actually need.