The ONLY difference between 'audio use' CD-Rs and 'general use' CD-Rs, apart from the price, is what type of recorder is allowed to use them.
Audio CD-Rs are allowed to work on 'audio CD recorders' - these are typically standalone hi-fi recorders, that can be directly connected to a home audio system. These recorders are required to reject any blank that is not authorised for audio use.
Computer-based CD-R(W) drives can usually record on any disc, regardless of authorisation.
The allowable use flag is part of the ATIP code which is recorded as a 'wobble' in the spiral pre-groove which is stamped into the disc during manufacture - this means that it is impossible to change a 'general use' disc into an 'audio use' disc, and that as audio players cannot read the ATIP, there is no difference in readability.
As for recording speed - you need to experiment to find the optimum speed for your recorder and media combination; slower is not necessarily better.