Power for 4-Star 40
There is more to consider than the engine size. There is also throttle control and prop size.
If you have progressed to where you can fly around along, land and do a little acro, I would recommend the .46FX with a few exceptions.
Certainly, with the right prop, you can get a good bit of straight line speed and, depending on your control hook up, you might get flutter. If you do go with the big engine, keep an ear out for the fatal buzz and watch your throttle.
As for prop size, I like climb myself instead of speed, so I like a lower pitch prop. You might try an 11-5, 11.5-4, 12.25-3.75 or 12-4 on your .46, if your gear is long enough. The latter 2 will give you great climb on a .46.
Another thing you need to do when you start flying powerful planes is to upgrade your control system. I am talking about 4-40 rods and clevices and sealing the hinge lines.
The OS .40FP will fly your plane and if you are still not sure of your skills or your reflexes are slow, it might be a good choice. It is an older engine and I think you might out grow it. If you wanted a plain bearing engine, I would recommend a Thunder Tiger .42GP.
Another choice is to start with the .40FP, but make sure your motor mount can be expanded to fit the larger .46FX. In this case, I would switch motor mounts to the Great Planes expandable motor mount, .40-.60 size. You can squeeze it in for the FP, then later widen it for the FX. I don't recall anyone else supplying this type mount with their kits, so if you start with the narrower engine, you might be stuck with a more complex job to upgrade.