Digistor 50 GB archive for life are manufactured by CMC Magnetics in Taiwan and have the mediacode CMCMAG DI6.
The quality can be decent with 6x speed on Pioneer writers from BDR206 on.
If you can get hold of them, I would prefer Mediarange BD-R50 6x with the same mediacode.
CMC Magnetics had quality problems with their BD-R50 discs around last christmas, which they seem to have overcome with actual Mediarange discs.
The quality of Mediarange BD-R50 currently is very good.