RE: Viper flying tips?
I do not recommend using the FIRE version engine on a Q-500 airframe.
Too much complexity, lots of drag, hard to properly mount the pipe. Just not worth it.
A SJ-50 with a swap to the LX muffler would be the better choice.
But to more directly answer the question, power wise, properly set up with a 8.8x8.75 on it, the FIRE50 setup would be just a little bit slower than a current 428 racing setup (160ish).
Also worth a reminder to others reading along here ....
please do not bolt a 428 engine or anything with that sort of power onto a stock out of the box ARF Viper.
There are threads documenting how do this, but it takes some work, modification, and modeling skills.