I'm reminded of this old post from 2009:
Originally Posted by Lindsay
Not too many prestretches at the Open, some with gut. I string for several Pro Circuit events throughout the year and I've charted tensions from various countries. The rule of thumb I've found is, if the player is American, expect their tension to be nearly 10 pounds higher than an international player. Of course, this isn't the gold standard and there are major exceptions, but its pretty close.
Edit: From 5 womens events and 3 mens events this summer, Americans are 8.3 pounds higher than everyone else.