Hi.

I say about 5 deg. up thrust is good. (rear of turbine up)
Take a look at the picture below. The angle of the turbine on that plane was spot on.

The angle doesn't really matter when you have good airspeed, but since the the engine is quite a bit above the centerline it wants to push the nose down when you trottle up on take-off or at low airspeeds.
Most people I see with Roo's have too little up-thrust on the turbine and what usually happens is the when they are on approch and find out they have to add power to reach the runway, the plane is pushed down to the ground by the thrust. This is a classic on aborted take-off's.