Stator Vane,
I don’t deal with the B737-300, but the general principle of the same for most Boeings. As the depth of the contaminant increases your Accelerate GO weight decreases, but your Accelerate STOP weight increases. The Accelerate STOP is the driving factor, thus you V1=V1MCG weight increases. (Try picturing a wheel ploughing through slush, it builds a wedge in front of the wheel which assists in stopping.)
You don’t go to the slippery runway chart, this is based on a totally different MU factor and generally gives you no stopping ability.
Which system are you following, the FAA or CAA?
Mutt.