Led Zeppelen and Dire Straits Japanese SHM CD's

Just my 2 cents on this subject.
I own a number of SHM-CDs including "Dire Straits, Brothers in Arms" which I think is outstanding.
However, in my experience the sound quality varies depending on the mastering used.
If the mastering is excellent the SHM-CD will sound just a bit better, icing on the cake if you will.
If the mastering is so-so the SHM-CD will not improve it enough to make a difference.
My caveat when purchasing these is; find out which mastering is being used, if you like it then purchase the SHM-CD, if not pass.
PS: I also own a number of HQCDs and Blu-spec CDs, same caveat applies. My favorites are the Blu-spec.
PSS: As far as I know; HQCD and SHM-CD are materials based while Blu-spec is a mastering technique.

Matjet,
There's another thread about sonic improvement with burn-in of the SACD-SHM discs. I'm not sure what I think about this reported phenomenon, I haven't experienced this with regular SHM-CDs. My feeling is that some other factors are at play here.
Perhaps you could read the thread and report on any such effects.
BTW: Most Japanese CDs have a date listed for the mastering used.