You have several options to work out how hard to hit your putts.
Have a look in the forums for RUNWME printable distance scales, covers most putter brands and meters, and the different meter speeds. Alternatively there are lots of formulas in the forums too.
Then if you combine this with the putter pal, or make your own with 10% increments, used together you then have a good guide re distance.
When using these you then need to factor in the slope on the greens, a very simple guide is to add a foot for each inch uphill, and subtract for down hill. As the greens speeds get faster, you will need to take more off, especially on very big slopes.
Good luck
KB
Printable Nike Daytona and Ghost Putter Distance Scales