Dick is spot on with his assessment in my expierence. It will be a nice but not really a slow model. Using a smaller engine won't make it slow and docile. The wing loading is the only thing that will do that. This same model built to around 6 lbs would be a slow and docile flyer much along the line of an old timer free flight with radio. At 8'ish lbs it'll fly and handle just fine but not be considered a slow model.

If you're only part way through the build and would share some pictures of the existing wing and the plans you're using to build the model from we could provide some critique on wood sizes. Also in particular if this design of yours uses a lot of big sheet wood parts then be super careful to weigh and select your wood for lightness. Just that alone can make a pound of difference on a model of this size.

Often times new designers over build by quite a bit in the hopes of making a stronger model. But this generally becomes a self fullfilling prophecy in that the heavier and stronger models often end up getting "tested" where a lighter model would not have stalled and spun or would have pulled up tighter or any other variation of the extra weight being the cause of the troubles where the lighter model would not have gotten into the situation in the first place.

If the thread takes a turn to concentrate on structure choices I'll move it over to the Scratch BUilding forum.