I don't know much on what has been done or proven or the numbers behind that, but I can give you my opinion from an engineering perspective. There is a difference with mandrel bending, there has to be, FROM THE CAT BACK. Its like any tube or pipe, it will only flow as well as it can from the smallest diameter. Take a straw for example, if the smallest constriction was 0.5 mm but the rest was 5mm in diameter, would you feel a difference in the pressure it would take to suck up water, it might not be noticible by a person drinking, but there is a larger % difference if measured.

You also have to remember that at the bends are where there is a decrease in velocity at the inner diameter of the apex and there is turbulance induced by this change in direction. Add a decrease in diameter or shape(and obstacle in it's path) in the pipe and you add even more turbulance.

So to answer your question on if it matters? It will for the air flow from the catalytic converter back, but then again, you are still resticted by the pipe from the exhaust manifold to the catalytic, and so madrel would not do anymore than the crush bend should have done because they are still both restricted from the front pipe.

For an intake it will help though, by how much I really don't know, depends on the difference in diameter you get, the car, and so many other factors.