A friend and I climbed the JPG Route in late July, and there was a ton of rockfall coming off the summit. We left early, but as soon as the sun came out it was on. Always looking up the whole time to avoid rocks. Thankfully nothing too large. We had to climb down into the bergschrund and back up the other side in order to access the summit block. Very interesting. I would suggest getting past the bergschrund just as the sun comes up. We descended via the Whitewater Glacier, and it was really straightforward. I can't compare it to any other descent route, since it's the only one I've taken. It took us 3 days in and out, and that was plenty of time.
Hope this helps some.