Put it this way, and I am speaking from experience as my husband ( I would catch a ride) would drive into North Point, via Sheung Wan to go to work from Lantau some days and return the same time as you are saying you will travel to HKIA. From Sheung Wan via taxi, this time is peak and always congested, no matter which tunnel you take, right through to Tsing Yi. I don't know if this is also a cost or time issue you are concerned about principally, but from experience ( picking up and dropping off clients from/ at HKIA), it is much cheaper and more convenient to take the airport express. It will still take about a hour or so to get to the airport by taxi as you have peak hour traffic during this time. If you are so intent on taking taxi, then leave at least 30 - 45 mins earlier. Even if the taxi driver is about to change shift, the option of the airport surcharge and a long fare may be enough to entice.
Cost isn't an issue. Timing cannot change. I guess its airport express in that case then.
So after two pages taxi isn't a viable option for that time.
If your starting point is further west than Shun Tak then I'd say taxi should be fine. The main bulk of the jams in Central are from Shun Tak all the way through to Admiratly (and beyond).
That would be a huge detour as I live on Lantau
What is more fascinating about this thread is that the car-person was saying take the train and the bus-person was saying take a taxi Have a good trip.