720x576 is MPEG-2 DVD quality for PAL video. The reason you can't find a card higher than this is because 720x576 is the frame size of PAL video and if it was resized any higher, especially from a Hi8 analogue camcorder tape, the picture would look blocky and/or stretched. Also people notice the poor analogue quality more on CRT and TFT computer screens, as they have more detail. A standard PAL TV set hides the bad quality a bit. If you record your Hi8 footage onto the computer in 720x576, transfer it to DVD and watch it on a regular TV then it will look fine as 720x576 is the standard resolution of a PAL colour TV.