After a successful clone of my OS-disk in 75 minutes with CloneZilla I tried to do the same with Ghost 4 Linux (G4L). I used the latest version 0.30 and used similar option to clone the disk/partition: source hdb1 -> sda1. Sda1 was again attached via USB using my usb/IDE adapter.
G4L managed to clone the disk in less than 15 minutes for 20GB. So almost 4 times faster than CloneZilla.
Booting with the new cloned disk did not give any problems.