Rip speed is mostly dependent on your CD drive...
On my machine I get 12-15x ripping, but at that speed it gets pretty sensitive to what else I do on the machine, so I've limited it max 8x rip speed where it's rarely affected by what else I do...

People seem to generally report 20-24+x rip speed with Plextors, which seems to be the drives held in best regard as to ripping.

/Michael