Yea I ran the a similar set up on the original Spear with a 3536 1200Kv and a 9x6 prop. The only difference on the 80% Spear was an 8x6. Plus the fact I made it an AET set up with the tail section hoping to stabilize it. Didn't work out for me. I am happy it worked out for you but unfortunately I won't be making a third. I will be moving into a different wing, haven't decided if it's the Versa because it's a tractor or the Goblin yet. What I am looking for is a good cam platform, and honestly I don't want the Versa because the prop is out front.
Mine just happens to be a tractor and I fly it with a "C" pack V2 and either a 3 or 4 S with a 9 X 4.7
If it was a pusher I would think you would need a lot of weight up front to get CG