I only have about 450 hours tailwheel time and a similar amount in tricycle undercarriages but I have also groundlooped, just once and have witnessed FNG groundloop at a pprune fly-in a couple of years ago at Popham.
Unless they are being grossly mishandled, tailwheel aircraft tend to groundloop as they slow down on the roll out; the rudder runs out of authority because of the reduction in airflow. In the Pushpak it was from 30 to 20 that it was most prone to swap ends - in the Pitts it is the decelleration through 40mph that it can misbehave.
Using asymetric the brakes is fine but use them with caution.
My groundloop occured at an estimated 20mph with quite a stiff wind. I'd flown in excess of 5 hours with 7 landings and was tired and could not wait to put the aeroplane away for the night and stop for a pint on my way home. As I landed at my home field, I slipped into that comfort zone that familiarity engenders. Did not concentrate as hard as I should have done and I reacted too slowly to all the warning signs - result a quick 270 turn and no damage to the aeroplane but my pride was seriously dented!
Stik