Here's some interesting pages that gives you some input on the stopping distances with ABS brakes and a comparison without them. While they are not Harleys, the results would be similar in results compared to non ABS bikes.
http://www.msf-usa.org/imsc/proceedings/a-Green-ComparisonofStoppingDistance.pdf
Brakes | National Highway Traffic Safety Administration(NHTSA) | U.S. Department of Transportation
ABS Brake Systems
Antilock Brake Systems (ABS) - AutoTrader.com
Antilock Braking Systems (ABS)
http://www.msf-usa.org/imsc/proceedings/a-Green-ComparisonofStoppingDistance.pdf
Brakes | National Highway Traffic Safety Administration(NHTSA) | U.S. Department of Transportation
ABS Brake Systems
Antilock Brake Systems (ABS) - AutoTrader.com
Antilock Braking Systems (ABS)