Hi,
two quite different tyres. No experience of the 12 on an XX , used them on a ZX11, IMHO not a cold / wet weather tyre. Best for winter was BT010 & now BT014 both again on ZX11 (Life 3.5Kmls rear, 7K front). Get good temp in them in less than a mile, and winter here is 4 months of under 10degC + rain. I know a few folks running a BT014 Front / BT020 rear combo on the ZX11 & they seem to be happy.
With tyres (tires!) being relatively cheap these days it might be worth going for the full set of 020's if you value mileage or the 014s if you want a fairly instant warm-up. The problem with a part worn front (57) is that the tread blocks are smaller & therefore wontt move around as much. It is this movement that largely contributes to heating the tyre & giving optimum grip.
Hope this helps
John