Let us not forget that an assumed temp. Is not allowed, and in this case, your tables should at no point give a V1 lower than V mcg. If still the case, this is a no go as the performance is inadequate for ake off.
One more thing, on contaminated runways, it sometimes is not so much the stopping distance that is the most limiting actor in v1 calculations, but rather the one engine acceleration disance between V1 and Vr due to the increased of drag. This is particulary true for slush covered runways.
When braking action is considered good and runway is not contaminated ( the 25% and 3mm. Definition), then Wet figures can be used in a lot of companies.