Since you used the terms "strong white flour" and "fast acting dry yeast", I assume that you are outside of the U.S., possibly the UK. But, even then, I don't see any reason why hand kneading about 11-12 ounces of dough by hand should be a problem. If you are trying to make the dough pass the windowpane test, I wouldn't be worried about not being able to pass that test. You would perhaps have to knead the dough considerably longer to develop the gluten to the point where you can successfully perform the windowpane test. It is OK for the dough to be slightly underkneaded and to allow biochemical gluten development to further develop the gluten. What brand of flour are you using, and did you warm up the last dough you made before using it to make the pizza?