Estas son "en resumen" las diferencias entre ambos modelos, de la magnífica tienda crtprojectors uk:

"In summary, the choice between BDP-80 and BDP-83 depends on the specific needs of the customer. The BDP-83 is recommended where the best possible video and audio performance is required. The BDP-80 excels in a home theater where an accurate digital transport is optimal, and it matches well with other home theater devices that offers quality video processing and audio D/A conversion. The BDP-80 is also recommended for smaller home theaters as a standalone player where universal media support and speedy operations are the most ideal."

Creo que lo explican bastante claro.

Y sí no pincha este link y podrás ver abajo del todo un cuadro detallado de las especificaciones técnicas de cada modelo (donde te dicen exactamente que el 83 sería el indicado para grandes diagonales, y el 80 para medianas y pequeñas):

http://www.crtprojectors.co.uk/oppo_bdp-80.htm