If none of the solulutions is quite what you are looking for, perhaps you could write a wrapper to FindStr that does exactly what you require?
FindStr is pretty good anyway so it should just be knocking a GUI up (if you want it) and providing a few extra features (like combining it with Find to find the count of files which contain a specified string [mentioned above]).
This, of course, assumes you have the requirement, time and inclination to do this!