Posted: 14/05/2015 at 21:12
I think you're more likely to get what you want from the hedge plants you've already got than by planting some huge things like the one in that last photo.
That photo shows a huge amount of foliage to be supported by a very small rootball - they're almost guaranteed to get transplant shock and loose at least half the leaves and look a mess - you'll have to cut them back too. And then there's a huge amount of foliage to catch the autumn and winter wind and rock the plant around, loosening the roots - rain will get in and freeze in the winter and cause all sorts of damage.
Stick with what you've got - treat them well, they'll put down a good root system which will give your hedge every opportunity to grow and grow and GROW.
I can't give you a guarantee, but I know which course of action I would take