I do just that using SuSE Linux 9.0 and K3b 0.10. Instead of 7 min a 700-MB CD is finished in 4:30 min.
Btw: Instead of 10X CD-RWs are burned at 15X.
The burner: Lite-On LTR-12101B.
Don't ask me why it's possible, I've got no idea.
I'm not kidding!