Essentially any wide setting will get distortion as its the final projection where its sorted out. Hence the images being nice once you sort the aspect in PS

Having just spoken to a friend here at work who was on Terminator 4, he was saying the plates were at 2048 x 1152 but after the reformat for output (with your black bars top and bottom) the ratio is actually 2048 x 1152.

Pixel size at the end of the day for output is entirely up to you yo can double it and treble it etc as long as it renders

hope this helps

Jay