You will never get the same quality at 1920 x 1080 as you do at 2560 x 1080. Apart from having a lot more pixels, the 2560 has the narrower field of view so collects more detail and runs at sensor resolution so doesn't get messed up by scaling.
If you want 1920 x 1080 video to keep or watch on TV then the best solution is to record at 2560x1080 and then chop 320 pixels off either side on your computer, that way you have the wide angle in the original for if you have an accident and need to show someone doing something they shouldn't out at the side but the version you keep for viewing is zoomed in to a fairly normal viewing angle and looks much nicer than actually recording at 1920 x 1080. VSDC free video editor is good for chopping the sides off.
If you do want 1920 x 1080 with wide angle then what is wrong with the 45 fps mode which does have 24 mbps? A 30 fps version of that would not give better video, or save any space so I don't see any advantage...
If you do have a good reason then maybe if you can explain it...