Quote Originally Posted by spackler
BC, is the distance variation due to the compression profiles of each ball? The ProV1X is a hard to compress ball, and thus rewards higher swing speeds and good ball striking with more rebound/distance. The TopFlite is an easy to compress ball, and as such acts as a governor on swing speeds by not compressing any further beyond a certain medium swing speed. Once the max rebound is reached, no further reward is given for higer swing speeds.

The above is on an 'off the driver' comparison. Off an iron, the slower swing speed (than the driver) would mean you would get better distance from an easier to compress ball. Hence the better distance from the TopFlite.
Your compression speculation is quite possible and a factor I did not consider. Even though my SS is not high(about 100mph) I still get more out of the X than the original ProV1.

It is possible, too, that the air temperature could be a factor? It seems to me that the X loses some ooomph when it's cold out, but the Topflite does not.