I think that this is going to be a subject answer at best - it would depend upon the surface it's being dropped onto, the angle it makes impact, and (most importantly) if ht surface is flat or corrugated in any way.
For example, if the phone lands touch screen down, and there is a rock right there that it lands on, it could easily shatter the touch screen. However, if the phone lands with the touch screen facing up, then it could potentially fall from as high as 6 feet and exhibit no detrimental effects.
The best thing about this shell holster combo (other than the kickstand which I'm addicted to) is the fact that it easily comes off so I can replace my discharged extended battery with a freshly charged one. But, at the same time, it seems to offer less of a rise from the touch screen as the shell holster combo for my DROID (which was a PITA to take off on a brand new one, until you had used (meaning removed and applied repeatedly) it for a few weeks.
But the kickstand is irreplaceable to me.