The video channels we use are roughly all the same theoretical bandwidth (about 6Mhz
including audio subcarrier or 4.x without), but 5.8Ghz gear makes better use of it, probably due to
better selectivity (sharper cutoffs at higher frequencies). When you see it in person,
it's hard to deny that the image quality looks a lot better. That is, when it's not
cutting out due to multi-pathing or blockage or flying behind or to the side of the high
gain Rx antena.
Most DVRs don't fully capture the difference in quality because they're bitrate limited
Note that true analog NTSC is really 525 scanlines, 486 of which are visible
and has no pre-defined horizontal resolution. 640x480 or 720x480 don't appear until
we enter the digital realm. There can be a lot more than 640 pixels worth of
information on a given analog scan line.