What is the drift rate of a VEX gyro?
Although I have not tested anything conclusively, I am fairly certain that it varies from around 1 to 2. Also, it depends on what programming software you are using. When I used the online Python on Robot Mesh or EasyC, there seemed to be a lot of drift, whereas with PROS the gyro worked with no significant drift as far as I could tell, especially in relation to the readings I had been getting with EasyC and Python.
A lot of times it depends on how fast your drivetrain is or how fast you make the robot go from turning to a complete stop. If you were turning with high speed drive motors at full speed then you tell the motors to stop instantly. Once the robot stops, the gyroscope would most probably be drifted from a range of anywhere between about 30-45 degrees.
QCC2 Blue Rooster had some conversion factors due to the voltages being different from the gyro. I think @jmmckinney has a newer library out there but I could not find it off hand.
https://vexforum.com/t/qcc2-gyro-and-pid-control-code/29292/1
In our December 2016 release of Robot Mesh Studio, we have tuned some of the internal parameters we used in the internal integration of the Gyro value in Python/Blockly. Using the Gyro with the newer release results in a far more stable reading with less jitter and less drift.