I have found that with most clubs hitting at 62% will produce at shot going at 50% of the max distance. I also tested a full set of G25 irons with standard balls and found that for each 1% reduction of hitting power (on meter), the shot would go 1.33% shorter. For example, a G25 pitching wedge has a max distance (on flat, no wind) of 115 yards and with rounding to nearest yard will hit as follows:
100% 115 yards
99% 113 yards
98% 112 yards
97% 110 yards
90% 100 yards
80%. 84 yards
70% 69 yards
etc.
i have also found that using balls with distance modifiers where each number of the modifier is treated as +1% is very accurate, so....
With Callaway Truvis balls with a +4 modifier, your 100% swing will be calculated by taking the 115 yards above and multiplying by 104% or 1.04 to get a max distance of 120 yards. This new chart would now be:
100% 120 Yards
99% 118 yards
98% 116 yards
97% 115 yards
90% 104 yards
80% 88 yards
70% 72 yards
62% 59 yards
60% 56 yards
Pretty simple to set up in a spreadsheet and adjust for different clubs. For every 3% drop in metered power your shot will travel 4% less. Thus multipliers would be .9866 at 99%, .9733 at 98%, .96 at 97%, etc.