I agree with Tony on the stab fences. On mine, I only have one set and the stall break is textbook straight as can be, but I run the Contra. I am debating whether to add a second set to eliminate the aileron differential required (I currently use -5% diff), because without it the plane was rolling "under itself" in the verticals. Rolls nicely now, and haven't noticed any secondary negative effects of the aileron diff anywhere else in the pattern.
John