With my limited understanding of Abhidhamma, I would like to say few things:
1) There can be approximately 600 citta vithi per second if all six senses are actively working, followed by 1800 manodvara citta vithi (3 mind door citta vithi follows every sense door citta vithi). Because human brain takes approximately 10 millisecond to process a sense input. And once brain send the signal (sanna) to mind (hadaya vattu), mind receives and instruct brain practically within billionth of a second or we can say that min do not need any time for processing a signal sent by brain.
2) While brain processes the sense input, mind is in bhavanga state and bhavanga citta arise at that time (i.e. bhavanga citta arise in the tune of billions per second).
So, we can say that per second (when mind is very active) 600 pancadvara citta vithi, 1800 manodvara citta vithi and billions of bhavanga citta flows. OR something close to this.