This is not really a good topic for the Beginners forum. You might get more/better responses if you posted this in the 3-D forum.

On another note....
I dont have personal experience with the GP .60 Extra, but a .91 4-stroke seems good. A good 3-D machine needs to be light, be overpowered, and have control surfaces with the ability to deflect enough for 3-D manuevers. While I'm pretty sure the GP Extra was not designed for 3-D, it can probably be used for it, though it might not be the best option. But here's a question for you: have you asked your friend if this is a good 3-D plane? Since you're buying it from a good friend, and you've seen him fly it, you would get the best information from him! While I'm sure you could get good answers from people on RCU that have flown this plane/engine combo, every plane is unique. You have direct access to seeing the plane fly, so I think asking your friend is your best option.