Yeah, What Kev stated is correct. 5.0 is one of the good ones, but it's more for a pilot like Szabo Jr., not someone that is just starting out to is still green.
2.1 has to be the best all around firmware that just works for the 3GX. 3.1 was okay, but hated the ground. 4 was good on the ground, but had massive tail issues in the air. then 5 has the twitch issues.
Stick with 2.1 until you can afford a better gyro. I'm pretty sure I have made all of the videos I'm going to make on the 3GX just because of all of the issues. Now, I need to find different gyros to play with other than ikon and BX.