Maskow
Veteran
Stage is stage and I won't believe that he really memorised 100 cubes if he won't say it 
I use loci method and for me 1 cube = 2 places, so 100 cubes = 200 places. (one place for edges and one place for corners)
You can't compare cubes with digits or cards, there are many reasons for it, really.
Look, I'm a speedcuber, I didn't spent much time on memorising digits but:
I can memorise cube in ~10 seconds (~10 words!) 1 word/sec
I can memorise 40 digits in 8-9 seconds (20 words!) 2.5 words/sec
I can memorise 37 cubes in ~32 minutes (~370 words) 11.56 words/minute
I can memorise 1000 digits in ~35 minutes (500 words!) 14.29 words/minute
Conclusion: Digits are much more easier in reading
Digits always will be faster.
A quick analysis of how much memorization this is: assuming each cube uses three-four locations in the Journey method.
100 cubes would result in ~350 locations. Using the same technique, a grandmaster of memory would use 350 locations for 3150 digits / 10500 binary digits / 38 to 39 decks of cards.
Some world records for these feats:
1-hour Digits: 2660
1-hour Cards: 28 decks
30-minute Binary: 4140
1-Day Cards: 59 decks
Certainly it could be challenging to someone without memory training to do it in a day, but a week would be very easy to do.
I use loci method and for me 1 cube = 2 places, so 100 cubes = 200 places. (one place for edges and one place for corners)
You can't compare cubes with digits or cards, there are many reasons for it, really.
Look, I'm a speedcuber, I didn't spent much time on memorising digits but:
I can memorise cube in ~10 seconds (~10 words!) 1 word/sec
I can memorise 40 digits in 8-9 seconds (20 words!) 2.5 words/sec
I can memorise 37 cubes in ~32 minutes (~370 words) 11.56 words/minute
I can memorise 1000 digits in ~35 minutes (500 words!) 14.29 words/minute
Conclusion: Digits are much more easier in reading