The only serious research I have seen into block size is Bitfury's
http://bitfury.com/content/5-white-papers-research/block-size-1.1.1.pdf


Look at the requirements for 32M blocks, 400GB daily, 128Gb ram.
At 32M, this excludes 95% of the current bitcoin nodes creating almost total miner centralisation.
Imagine what 6Gb blocks require.



I take these figures with due scepticism, but there is nothing else to compare it against.