Use the lowest compression available.
The "dirtier" the signal, the harder the work the CODEC has to do, and you could end up with a complete mess. Again, use DVD RWs for trial and error. Do not expect to fit six hours on a single layer disc. What makes up the total six hours? Aim to fit one program per disc. If a single program runs for two hours, then you may have to fit it across two discs.