You used to be able to get something called TT dynamic which measured dynamic range, but you can't get it free any more. You can use something like voxengo span.
Theres a bit of a thread hereviewtopic.php?f=1&t=184573&hilit=+span+dynamic
and you can search the forum for dynamic range.
It's all relative anyway. Over-compressed generally means the dynamic range has been reduced. So if you simply deduct the RMS from the peak for different tracks you should get an idea. You will probably find a low value on commercial stuff, but I cold be wrong, they may have ways to get around it, like keeping the structure very simple. Radio tracks are heavily compressed, partly by the radio stations themselves I think.