In the Juve Vs flail example, the Juve rolled 4, getting a 6 on the dice.Fighter (7-3+) so WS 4, plus die 2, +1 charging, -1 fumble equals 6.
Juve (7-5+) so WS 2, plus die 2, -1 fumble equals 3.
I can appreciate the desire for such a system, but ultimately I disagree with others.
As mentioned, melee is a high risk/high reward strategy. Due to random rolls, premeasuring doesn't really change that -but this almost universally reduces the possible effects.
CGC becomes all but untouchable in melee, especially since you have to make a willpower check to even target them in the first place.
I like the simple solution of opposed rolls, but in the same vein as toughness.
So WS 2+ would hit WS3+ on 3s, and 4+ on 2s.
You could do the 7-WS thing as well.