Is it common for super grandmasters to have the ability to play simultaneous blindfold chess? Magnus Carlsen against 10 blindfolded. Timur Gareev plays 30 players blindfolded. I was wondering if these super grandmasters all can at least play 7 masters blindfolded and beat them.
This is more a comment than an answer.

The attached fragment is Mikhail Tal commenting  his blindfold simul against 10 first category (approximately 1800-2000 Elo) players - as the match goes, board by board. The fragment is a part of 1968 documentary on limits of human mental abilities.

The movie is in Russian; if there is an interest, I may try to translate.