Cutting a Custom Threshold: Best Tool for the Job?
Yeah, that 4" would be a long cut.  It could be done in two passes, one from each side.  The middle area would have a bit of an overlap and maybe a blade mark, but that could be sanded down.  Plus you are probably going to finish it anyways.

What I would recommend though is changing the shape of your transition piece to make it easier to cut, and would also make it more pleasant to walk ok.  I posted a similar question regarding a transition from tile to hardwood.  Although your question is different, some of the answers there might help you out.  For example, take a look at the shape of this transition piece:



In your case, this would be 3 separate cuts instead of one long one.  Also the flat top surface will make it more pleasant to walk on vs. the angle (point) you have at the top of your example.