I have tested CD-Rs on two different recorders at various recording speeds.
I would recommend 4x as this produces the lowest BLER for most of the discs
tested.  Discs these days are not optimized for low speed writing such as

Joe Iraci
Conservation Scientist
Canadian Conservation Institute

I make my CDs at 2 or 4x.  I note those  presently aalable go up 56x or so.

Is there any reason these won't perform well when  recorded more slowly?  I
can't imagine why they wouldn't but better  safe...

Steve Smolian