I'm rethinking this. Rockwool is basically hydro so I would keep it near 5.5 until planting in soil. Actually .5-1.0 pt won't make much of a difference either way at this point.
their is so many ways of cloning and different products to use all i can say is take what was said and do what you do things will work it all an experiment if you have never cloned before. always cut more then you need and your chances of rooting what you want is greater.