It's the stopping I've generally had problems with, not traction.
In lots of slush I've had the ABS warning light coming on (sensors don't like being too cold?)
In really slippery conditions the system also seems to get confused when the wheels turn at different rates and the warning light also comes on.
So unless I've been very unlucky with my 2 156s I reckon the ABS is fine except in winter ! Although thinking about it I've also got the warning light when I had to drive with the spacesaver on which I guess is a different diameter to the other wheels....
Alfa GT JTS Selespeed. Previously 2.0TS Sele Sportwagon, 1.8TS 156