RE: Goldberg Matrix
I used the 12x4W on my 50SX's and it was a great combo. You might get away with the 13x4W but it might not allow the engine to spool up quick enough for 3D. When running a 2-stroke for 3D you need to get the rev's to get into your power curve, if you get into trouble you need those rev's right now!
I'll be going out of town tomorrow morning until Saturday, so if there is any more questions, I'm not ignoring you, I will answer when I get back.
Good luck to all and FLY 'EM HARD!!!!
Ken