Looking for information and guidance on the radical pruning of Tall Oak Tree...
Topping trees is NOT a recommended pruning practice. This stresses the tree, can cause the growth of weak suckers that break off when they become heavy branches and wood rots can be a problem. If a tree is too tall you may need to consider removal. Or if the tree must be reduced in size use the crown reduction technique. See our publication on pruning techniques for mature trees http://extension.umd.edu/sites/default/files/_images/programs/hgic/Publications/HG84_Pruning%20ornam...
and the link from the International Society of Arboriculture regarding topping trees
At this point you should contact several certified arborists for an onsite diagnosis of your tree regarding best pruning practices http://www.treesaregood.org/