Thanks Ian W for pointing me to " Multiple resources and performance prediction" (Wickens, 2002)
http://sunburst.usd.edu/~schieber/ps...ckens2002b.pdf
some heavy reading...jumping to the conclusion:
"Basic psychology and neurophysiology must identify the characteristics of human information processing that make such endeavours more, or less, successful. The analysis and prediction of human productivity and safety in high workload environments requires models to predict such di€fferences."
In summary, scientists are starting to understand more about "cognitive overload", and there are some interesting theories, yet - more research is needed.