I think that you can go with a bigger cut with this one, though it also depends on it you are going to cross the lines or not as well, if you are not then you are going to loose some fabric on each end, but it is a personal choice, the bigger the cut the more loss you will have.
If you are sticking within each block I would divide it as close as you can to the block size to get the optimum space used, so 4inches which will give you 4 across or 5 inches which will give you 3 across. though 5 might be a bit big for this,
if you are using the side piece as well for blocks you will want to go a little bit smaller, as it is smaller there,