I have a 30hp Mercury (actually Tohatsu) - I believe in the 40hp range Mercury made by Mercury so different motor from 40hp Tohatsu.  Tohatsu 30hp is a sweet little motor - love it.  I bought the Mercury badge as 5yr warranty offered by Mercury against 3 year Tohatsu warranty for similar price.  Are warranties on offer all the same?

Pull start 40hp would have to be 2 stroke I think. Pull start 4's go up to 30hp.

The Yamaha, is it the 2cyl CV? If it is, go for the 3cyl Merchatsu, far better and smoother motor. There is also a Merc 40 that is US built and again, only 2 cylinder and no where near as good as the Japanese models.

The Tohatsu / Merc Lightning XR 40hp runs rings around those models IMO. The 3cyl Yamaha is a beautiful motor, but costs nearly as much as a 4-stroke and I cannot fathom why they ask so much for them! There is thousands of happy Tohatsu / Mercury 40 owners in the country, they are a de-tuned 50hp and go like stink with awesome reliability.