early sexing is only really an issue if you're flowering cabinet is limited in space. if it's not, as said, you'll be able to tell long before it's an issue, and it really is the difference between black and white.
another method, although a bit of a painstaking one, is to take 10 cones, one from each, label accurately, then just force these straight into flower the moment they root. you can then look at them, tick off 1 3 5 and 9 as being the females, and as such only keep the corresponding "mother plants"