on the exchange side - market data/trade/ack latencies can be microsec in the 50th percentile, single digit msec in the 90th, and double digit msec in the 99.99

on the exchange side - market data/trade/ack latencies can be microsec in the 50th percentile, single digit msec in the 90th, and double digit msec in the 99.99th, the variance can be significant and also change based on hr of the day and how well the exchange handles the load. So even if you use customized, co-located hardware/FPGAs or even ASICs with the fastest interconnects and unlimited bandwidth and your engine responds in nanosec, still the message you get from/send to an exchange can sit there in a queue for something like eternity.