Interesting question. A basketball to rim is less than 2x, so 2.5 seems generous. Never-the-less, I voted a bit larger.
What would be an interesting study would be to see if more putts are made with a 5" diameter hole . On theory the obvious answer is yes. But I wonder if the additional margin of error eventually
Not necessarily true. Grounding the club when your ball lies in rough is equally risky. By not grounding the club, if the ball moves when the player did not even touch the grass near it, I would be inclined to rule it as a act of God. If he grounds the club or takes a practice swing in the immediate vicinity, then I call the penalty. That is still true even under the theoretically less penal rule in today's rule book. Reverting to the previous version wouldn't change that in any significant way.
I have been in a windy situation where the ball sitting up in heavy rough never really seemed to be at rest - it was sort of fluttering with the wind gusts that were moving the grass. I've also seen a player be penalized (correctly) for causing a ball lying in fairway grass to move after taking a practice swing more than a foot away from the ball.
Every ruling must be treated as a unique incident, and the more you allow the referee latitude in making his decision, the more subjective the rule becomes.
Techniques are usually subjective and personal. Some sheer voodoo. I find that I tend to spend too much time frozen over a putt and it usually just misses on one side or the other and rolls about two feet past the hole. Lately I've been experimenting with a method that seems to relieve tension. Standing over a putt, I might make two practice swings, line up the putt. Then I turn my head towards the target,ascribing an imaginary line i wish to take with my nose. I then retrace that line back to the ball and when my nose is directly over the ball, I take the putter back and make the stroke. No time to think about it, no hesitation, just follow the line, make nasal contact (figuratively) and execute. My nose does not extend back beyond the ball however. I know, sounds ridiculous, but seems to work. I seem to recall reading something similar years back where the player looked twice to the target, and executed immediately during the second "look" as a trigger move.