VAP,
I understand perfectly for starters... BUT (you had to know it was coming...

)
Supposed you have a soft touch shot that on a scale of 1-10 was a 2, and all of your practice strokes are a 5. IMO practice strokes build a (temporary) muscle memory for the shot ahead, and if you have built a muscle memory for a 5 stroke, and then try to deliver a 2, your arm/stroke wouldn't be prepared for it.
Same goes for using a "5" practice stroke on a power shot that would be delivered with an 8-10 stroke. I don't think that your arm/stroke would be prepared for it.
I guess what i am getting at, is that if you have "visualized" the shot; you must have "visualized" the final stroke, and if your practice strokes aren't what you "visualized", then what good was the "visualization"?
In the future, if anybody asks you if you know of anybody who's practice strokes are the same speed as their final stroke, you think of me

.
Thanks,
Jon