Let me define a high frequency automated trading system, keep in mind I have seen human traders input in 10-15 trades in < 3-5 seconds. I would classify high-frequency trading systems at least at 100 trades a day (and that would be considered small). The few decent sized hedge funds that I have some knowledge of generates 10k or so trades a day.
I know of at least one firm averaging 80 million shares traded a day across all stocks.. not sure how many symbols they trade.
right now to do more than 500 trades a day when screening 200 symbols. what platforms are you using ? how many symbols? my win% ratio for the papertrading the last few month is 40% and it's profitable (including comm. and with no slippage)
I have seen working models that work on small baskets of symbols. That works pretty well because at the time the spread was wider in general and it was a firm's account trading the models thus the transaction cost is next to nothing. And the frequency of trades is very high during market opens and closes. We are talking about 10 to 20 trades across 20 to 30 symbols done within a few minutes whenever the conditions are met. That was quite an amazing thing to just watch these bots trade