imho, Thomas posting summarized it pretty well. I've been using Provia and AgfaPhoto CT 100 Precisa, which is said to be Fuji Trebi (the japanese consumer version of Provia), in 35mm, but its cool rendering never grew on me. When I read about Provia 400 having a different character, I tried it in 645 and was pleasantly surprised. I prefer its rendering to the 100 ISO version and it is a great film. The ISO 400 sensivity comes great when shooting my 645 Pentax 35mm-like and absolut resolution is of second importance.
The difference is more obvious when scanning both films at high resolution. So far, I scan my 120 films at home with real 1.200dpi and under these circumstances, the Provia does not seem to suffer from any drawback compared to its less sensitive family member. But once to amp up the resolution, the increased grain and lowered resolution is visible. So it depends on the final usage. Each has its own use.