Assuming you’re looking for the difference between the Dash 8 300 and the Dash 8 Q400:
DASH 8 300 – Range, Max Cruising Speed & Max Operating Altitude
The Dash 8 300 range is 924 nautical miles (1.711 km).
The Max cruising speed is 287 kts (532 km/h).
The Max Operating Altitude is 25,000 feet (7.600 m) above mean sea level.
DASH 8 Q400 – Range, Max Cruising Speed & Max Operating Altitude
The Dash 8 Q400 range is 1.100 nautical miles (2.040 km).
The Max cruising speed is 360 kts (667 km/h).
The Max Operating Altitude is 27,000 feet (8.230 m) above mean sea level.
The Q-400 is also 7 meters longer, and 1 meter wider (wingspan), as well as the ability to accomodate 30 more passengers.
Source: Quora