This picture (click on picture to enlarge) was taken from the site of PA1B a very nice site about QRPp. What makes you think you can't be heard with QRP? The difference between 500 milliwatt and 100 watt is only 4 S-points. When someone with 100 watt is S9 or S9+ you must be able to work him with QRP. Avoid huge pile ups, because that will be hard. I do not say it's impossible. It's a little bit harder to come through. I am not only QRV on the QRP frequencies. I just wander around on the entire CW band. Even I am not always mention that I am working QRP. If they hear me is OK for me. When the opposite station is very weak, then it would be difficult to be heard. But also not IMPOSSIBLE! Sometimes they hear me with 5 watt, even when that station is weak and almost in the noise. Just try, you never know.