I do a lot of Audio CD burning as I have a recording studio. I use 8X as my audio CD burn speed "standard". This allows compatibility with almost all audio CD players. I've been using the 8X for about 10 years and have burned hundreds of audio CD-R's and have never had a CD come back as "unplayable" or "skipping". I only use JVC-Taiyo Yuden "Professional" ink jet printable CD-R blanks, but the brand does not dictate the burn speed, its the drive.
The burn speeds are hardware dependent. e.g. most SATA CD/DVD burners will only go do wn to 16X (except one model LG CD/DVD burner). PATA (IDE) burners of recent production will go down to 8X for audio CD burning. Although there may be some software utility that will change/lower speeds, I havent found one. I have Nero and use Nero Burning ROM for all my CD Burning. I have a bank of 5 USB connected PATA burners that I use for my CD production.
With CD burning software, you must have a CD-R blank loaded in the drive BEFORE you attempt to burn, so you can set the burn speed. If you try to set the burn speed first, without a disc in the drive it will only default to its highest burn speed.
Other recording engineers, that I've talked to on recording forums agree on the 8X speed.
The only CD burner drives that I know that will burn at 4X are very old (obsolete/out of production) PATA (IDE) drives. The last one I had was one that came with a Windows 98 PC.