I haven't checked it on any of my bows lately but I generally follow 1.75 fps for every pound of draw weight changed. I may need to update that figure though as it seems many of the normal generalizations seem to have changed with the changing efficiency levels of today's bow setups. I currently have my Old Glory at a 60 pound draw weight but would be willing to turn it up to 70 to see what type of speed change results....assuming the arrow is still properly spined. However, those results would only be indicative of that particular bow with that particular setup....though it would at least be a good place to start.

I did not notice that particular statement but is it possible that they are referring to the difference in speed between a 60 pound bow shooting a 300 grain arrow versus a 70 pound bow shooting a 350 grain arrow?