Are you suggesting, or asking, if the 1080 pixels would fit just inside the 1200 pixels of the 23"? Whereas the 30" would either resample to get a larger display--and resampling is not something we like, pixel for pixel is better--or simply have "wasted" pixels? Is this the way to look at it?
Would the 23" nearly give pixel for pixel for 1080?
It doesn't matter, all three will do the same great job. A pixel is a pixel. All three will look the same. I use a 30" and a 23", both do great jobs. As for how big the window playing your footage, depends on what resolution you have the monitor set for. Higher resolutions will give you smaller windows, but it's still a pixel for a pixel. All three will do the same job just as well.