Well, having flown Dash-8 100/300/Q400, I can say from experience that the aircraft can handle a LOT of ice. The Q400 also has an ice detection system, alerting the crew through the centre MFD (Engine Display). "ICE DETECTED" will flash in reverse video for 5 seconds, go to steady reverse video, then turn white/normal video when the "increased ref speed"-switch switched ON. The warning activates when either of the two ice detector probes (on on each side of the a/c nose) detect ice of more than 0.5mm thick, and are very sensitive.
The de-ice boots are, as per manufacturer´s recommendations, to be activated before entering icing conditions. These are very effective at removing ice. Never had any problems with this system during my 6 years on DHC8 models. Also, two small spigots (one on each wiper) will tell you if ice is accumulating. These are part of the certified ice detection system, and are lighted (on/off btn).