DAS used to write for a magazine that was called 'Instinctive Archery'. He had an article in there about this subject. With a .500 spined arrow 1/2 inch of arrow equaled 50 grains of point weight.
His email address was listed in the article and I asked if that held true for .600 or .400 which I was shooting at the time. He responded with 'I only tested .500'.
Now, with a little more experience under my belt, I'd question his premise. I'm not sure going from 125 to 175 would be the same as going from 300 to 350? I'd only question it, he very well could be on the money.
If it wasn't hunting season I'd look for the article.