Note 750*1000^3 disk maker = 699*1024^3 customary.
I find MPEG-2 HD to be 4000 MB/hr, MPEG-4 HD 2100 to 2600, MPEG-2 SD 900, OTA is higher.
That is with filler and before commercials.
So 699*1024/2400 (say) = 298 MPEG-4 hours with some filler.
With my mix of MPEG-2 HD/SD, MPEG-4 HD, and little OTA, I get 300 to 320 hours of programs on each "750GB" disk.
-Ken