The pros to using a curved screen with an A lens is that you can set the curve to compensate for the pincushion caused by the lens. If you have a long throw set up then the pincushion becomes very small, so you need to consider this.
The con of using a curved screen without a lens (and this includes sliding the lens out of the way for 16:9 content) is that the image will overspill the middle top and bottom of the screen so it will look a bit like a barrel laid on it's side if you follow? There is no benefit to using a curved screen without a lens apart from arguably that it looks cool and might not direct as much light to the side walls as a flat screen would if the room is less than ideal. However, if you can accommodate a fixed curved screen, then I guess that it is a dedicated room and therefore should have black side walls and ceiling at least near the screen.
If you have a lens and curved screen, then you will have to leave the lens in place the whole time so it is compromising 16:9 viewing as this will be scaled down to 1400 x 1080 (approx). Therefore I think that it's a better solution to have a long throw set up with minimal pincushion to start with and then use a flat screen (or at least the curved screen could be so slight that 16:9 content could be viewed without the lens in place.
"Don't believe everything you read on the internet". William Shakespeare 1615