What volume are you going to brew to? As I found out if going for the full 23L this will be a bit weak around 3.7 - 4 % ABV depending as to how well the yeast attenuates.
Brew to 20L and it will come in around 4.3 - 4.5 %
Next time I make this I plan to brew to 20L and use 1.5kg of Dark LME + a tin of black treacle (454g). Should make a more robust 5.3 - 5.7 %.