Vegging 2 weeks there's a good chance they'll be a foot at the inception of flower. lol!
What you need to do is look up the amount of 'stretch' of that strain. It's a popular one over at icmag; look in the grow log section and see how much it stretches in the first week of flower.
How large a light are you using on these 40 clones? I hope it's a 1000hps; if it's smaller, you are going to want to flip them immediately because otherwise good luck fitting them in the light's footprint.