No takers, huh?
Oh well, I changed my mind in the meantime and will stick to the 160 for now.
I did find this http://wl500g.info/archive/index.php/t-8442.html thread which also points back to a thread from these forums.
I got as far as making the 300Gb disk a mirror of the 160, but it was not clear to me if I could have then just loaded the copy and booted from it alone, nor was I sure about using the rest of the disk not used in the mirroring.
Another time perhaps.
JOC