Is there a way to change the Ctrl+mousewheel zoom rate ?
First, look at the recent similar post:
Of course, instead of doing nothing when the Control key modifier is in effect, you can do something similar to what GoView.DoWheel does:
PointF oldpos = this.DocPosition;
this.DocScale *= (1 + ((float)evt.Delta)/2400);
PointF focus = ConvertViewToDoc(evt.ViewPoint);
this.DocPosition = new PointF(oldpos.X + evt.DocPoint.X - focus.X, oldpos.Y + evt.DocPoint.Y - focus.Y);
But you can change the 2400 value to something that suits you better.
I implemented the desired zoom behavior in a GoView.DoMouseWheel override.