Burning Speeds



I am a new owner , (and very much a Newby) ,of
(1) A Panasonic DVD Recorder Model DMR-ES30VEB which also incorporates VHS Recording facility.
(2) A Panasonic DVD Recorder Model DMR-E50.

My problem is that, whilst I know which Disc Format to use ie. DVD-RAM, DVD-R or RW,I am confused as to which disc speed is appropriate, ie. 4x, 8x etc. I have checked the handbook for both models but cannot find any suggestions or details of the type of Burner installed.

Can anyone enlighten me please?