While I'm very methodical with grids, flows, vertexes, and angles (even use Jruler to measure exact break in single player) I've always found my distance by feel.
On stimp 12 with a putt 25F and 5 inches below my feet I do something like 25 - 5 = 20 and then I randomly take off what I think is necessary. In the above case probably hit the ball for 17F which should be around 1-1.5 F past hole.
On 40F and 11 inches below my feet I'd 40 - 11 = 29 and take off around 5-6F more for an adjusted putt of 24 or 25F. No clue if this is good or bad ;). It's just how I do it. Besides, green speeds seem to change quite often, just like the Wind. It's never the same forumla so I prefer to make "feel" based decision for distance.