if you want to RX datv.... the bigger dish the better.
the current transmission is using QPSK with 1/2 fec.
only 1 dB c/n is needed to view it now. thats why many people can rx it.
But if you use such a low spectrum density at 333Ks or worse 125Ks
we are talking more about sstv then....instead of atv.
So i go for quality.... and thus you need more db's at rx'ing point...
So the bigger, the more transmissions you will be able to see....
Even the higher quality ones.
HD at 9mbits/s will not be possible... unless you had very very high power and a very very big dish!